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Liu, Teng, Peng-Fei Lu, Bi-Ying Hu, Hao Wu, Qi-Feng Lao, Ji Bian, Yang Liu, Feng Zhu i Le Luo. "Phonon-mediated many-body quantum entanglement and logic gates in ion traps". Acta Physica Sinica 71, nr 8 (2022): 1. http://dx.doi.org/10.7498/aps.71.20220360.
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The implementation of high-fidelity multi-ion entangled states and quantum gates are the basis for ion trap quantum computing. There are developed quantum gate experimental schemes for realizing multi-ion entanglement and quantum gate, such as Mølmer-Sørensen Gate and Cirac-Zoller Gate; In recent years, there are also ultrafast entanglement gates that operate outside the Lamb-Dicke regime by designing ultrafast pulse sequences. In this typical many-body quantum system, these entanglement gate schemes all couple the spin states between ions by driving the phonon energy level or motion state of the ion chain. To improve the fidelity of quantum gates, they all use modulated laser pulses or appropriately designed pulse sequences to decouple the multi-mode motion states. In this review, we summarize and analyze the essential aspects of the realization of these entanglement gate schemes from the theories and experiments, and we also reveal the basic physical process of realizing quantum gates through nonlinear interactions in non-equilibrium processes by driving ion chain motion states.
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Wen, Zhiyuan, Jiaheng Li, Ziqiang Wang, Yong Xu i Jing Zhu. "Soft-mode-phonon-mediated insulator–superconductor transition in doped two-dimensional topological insulator RuC". Applied Physics Letters 121, nr 1 (4.07.2022): 013102. http://dx.doi.org/10.1063/5.0095044.
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Recently, the search of superconducting materials with topological states has attracted extensive interest due to their exotic properties. By using first-principles calculations, we predict that RuC monolayer is a two-dimensional topological insulator (TI) and shows a TI–superconductor transition under electron doping, leading to a superconducting transition temperature Tc of 1.4 K. Further analysis reveals that the emergence of superconductivity in RuC depends critically on the existence of flatband optical phonons as well as the appearance of multiple electron-pockets and phonon mode softening induced by doping. Moreover, we find that Li-intercalated RuC (LiRuC) is a thermal dynamically stable, superconducting material with a high Tc of 9.8 K, benefitting from the strong electron–phonon coupling. Many other superconductors with flat phonon bands are also predicted via elemental substitution in LiRuC. Our results will broaden the research interest in exploring more superconductors and modulating their physical properties through flat phonon bands.
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Bastarrachea-Magnani, Miguel Angel, Jannie Thomsen, Arturo Camacho-Guardian i Georg M. Bruun. "Polaritons in an Electron Gas—Quasiparticles and Landau Effective Interactions". Atoms 9, nr 4 (16.10.2021): 81. http://dx.doi.org/10.3390/atoms9040081.
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Two-dimensional semiconductors inside optical microcavities have emerged as a versatile platform to explore new hybrid light–matter quantum states. A strong light–matter coupling leads to the formation of exciton-polaritons, which in turn interact with the surrounding electron gas to form quasiparticles called polaron-polaritons. Here, we develop a general microscopic framework to calculate the properties of these quasiparticles, such as their energy and the interactions between them. From this, we give microscopic expressions for the parameters entering a Landau theory for the polaron-polaritons, which offers a simple yet powerful way to describe such interacting light–matter many-body systems. As an example of the application of our framework, we then use the ladder approximation to explore the properties of the polaron-polaritons. Furthermore, we show that they can be measured in a non-demolition way via the light transmission/reflection spectrum of the system. Finally, we demonstrate that the Landau effective interaction mediated by electron-hole excitations is attractive leading to red shifts of the polaron-polaritons. Our work provides a systematic framework to study exciton-polaritons in electronically doped two-dimensional materials such as novel van der Waals heterostructures.
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Elsaesser, Thomas. "Structural dynamics of ionic materials mapped by femtosecond x-ray diffraction". Acta Crystallographica Section A Foundations and Advances 70, a1 (5.08.2014): C769. http://dx.doi.org/10.1107/s2053273314092304.
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Relocation of electronic charge plays a key role for functional processes in condensed-phase molecular materials. X-ray diffraction with a femtosecond time resolution allows for spatially resolving transient atomic arrangements and charge distributions [1]. In particular, time-dependent spatial maps of electron density have been derived from x-ray powder diffraction patterns measured with a 100 fs time resolution. In this talk, new results on electron dynamics in transition metal complexes and on field-driven charge relocations in elementary ionic materials will be presented. Crystals containing a dense array of Fe(II)-tris(bipyridine) complexes and their PF6 counterions display pronounced changes of electron density that occur within the first 100 fs after two photon excitation of a small fraction of the complexes [2]. Electron density maps reveal a transfer of electronic charge from the Fe atoms and - so far unknown - from the PF6 counterions to the bipyridine units. The charge transfer displays pronounced Coulomb-mediated many-body features, affecting approximately 30 complexes around the directly excited one. As a second topic, electron relocations induced by strong external optical fields will be discussed [1,3]. This interaction mechanism allows for generating coherent superpositions of valence and conduction band quantum states and inducing fully reversible charge dynamics. While the materials LiBH4 and NaBH4 display electron relocations from the (BH4)- ions to the neighboring Li+ and Na+ ions, LiH exhibits an electron transfer from Li to H. The latter is a manifestation of electron correlations and in agreement with theoretical calculations.
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Ding, Hao, Yuwen Hu, Mallika T. Randeria, Silas Hoffman, Oindrila Deb, Jelena Klinovaja, Daniel Loss i Ali Yazdani. "Tuning interactions between spins in a superconductor". Proceedings of the National Academy of Sciences 118, nr 14 (29.03.2021): e2024837118. http://dx.doi.org/10.1073/pnas.2024837118.
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Novel many-body and topological electronic phases can be created in assemblies of interacting spins coupled to a superconductor, such as one-dimensional topological superconductors with Majorana zero modes (MZMs) at their ends. Understanding and controlling interactions between spins and the emergent band structure of the in-gap Yu–Shiba–Rusinov (YSR) states they induce in a superconductor are fundamental for engineering such phases. Here, by precisely positioning magnetic adatoms with a scanning tunneling microscope (STM), we demonstrate both the tunability of exchange interaction between spins and precise control of the hybridization of YSR states they induce on the surface of a bismuth (Bi) thin film that is made superconducting with the proximity effect. In this platform, depending on the separation of spins, the interplay among Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction, spin–orbit coupling, and surface magnetic anisotropy stabilizes different types of spin alignments. Using high-resolution STM spectroscopy at millikelvin temperatures, we probe these spin alignments through monitoring the spin-induced YSR states and their energy splitting. Such measurements also reveal a quantum phase transition between the ground states with different electron number parity for a pair of spins in a superconductor tuned by their separation. Experiments on larger assemblies show that spin–spin interactions can be mediated in a superconductor over long distances. Our results show that controlling hybridization of the YSR states in this platform provides the possibility of engineering the band structure of such states for creating topological phases.
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Gupta, Anushri, Sanjeev K. Verma, Anita Kumari i B. D. Indu. "Generalized phonon density of states of La2−xSrxCuO4 cuprate superconductor". International Journal of Modern Physics B 33, nr 28 (10.11.2019): 1950328. http://dx.doi.org/10.1142/s0217979219503284.
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Many body quantum dynamics of phonons is steadily developed by considering the various effects of anharmonicities, defects (consider as doping or impurity concentration) and electron–phonon interactions in model Hamiltonian (instead of BCS Hamiltonian) for a high-temperature superconductor (HTS). This enables to obtain the expressions for the renormalized phonon spectrum, the renormalized phonon density of states (RPDOS). The RPDOS can be resolved into diagonal and nondiagonal parts where the nondiagonal component is found highly impurity-dependent. Considering the suitable Born–Mayer–Huggins (BMH) interaction potential, the renormalized phonon spectrum, RPDOS and generalized phonon density of states (GPDOS) of the La[Formula: see text]Sr[Formula: see text]CuO4 layered superconductor have been numerically analyzed and it was found that these quantities depend on doping concentration, anharmonicities, and temperature. The results are compared with the inelastic neutron scattering experimental data of GPDOS for La[Formula: see text]Sr[Formula: see text]CuO4 and are found in good agreement. The ratio of deviation in GPDOS to GPDOS at critical temperature ([Formula: see text] K) shows the implicit difference at [Formula: see text]. The impact of defects, anharmonicities, and electron–phonon interactions in the cuprate superconductors virtually modify the scenario of GPDOS and affirm a large number of exotic peaks in the spectrum.
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HU, BEN YU-KUANG. "MANY-BODY EFFECTS IN FRICTIONAL DRAG BETWEEN COUPLED TWO-DIMENSIONAL ELECTRON SYSTEMS". International Journal of Modern Physics B 13, nr 05n06 (10.03.1999): 469–78. http://dx.doi.org/10.1142/s0217979299000369.
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Independently contacted coupled quantum wells separated by barriers which allow significant interlayer interactions but no tunneling have been fabricated. When current is passed through one layer, the interlayer interactions drag carriers in the second layer, resulting in a voltage response (for open circuits). The magnitude of the response gives a quantitative measure of the effective interlayer interactions and response functions of the system, and hence this is an excellent laboratory for the study of many-body phenomena in two-dimensional electron gases. We review the Boltzmann and Kubo formalisms for the theory of drag effects in coupled quantum wells and discuss three specific cases where many-body effects significantly affect the drag: (1) acoustic phonon-mediated drag, (2) large enhancements due to coupled plasmon modes, and (3) interplay of screening and Landau levels in large magnetic fields.
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Jang, Joonho, Heun Mo Yoo, L. N. Pfeiffer, K. W. West, K. W. Baldwin i Raymond C. Ashoori. "Full momentum- and energy-resolved spectral function of a 2D electronic system". Science 358, nr 6365 (16.11.2017): 901–6. http://dx.doi.org/10.1126/science.aam7073.
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The single-particle spectral function measures the density of electronic states in a material as a function of both momentum and energy, providing central insights into strongly correlated electron phenomena. Here we demonstrate a high-resolution method for measuring the full momentum- and energy-resolved electronic spectral function of a two-dimensional (2D) electronic system embedded in a semiconductor. The technique remains operational in the presence of large externally applied magnetic fields and functions even for electronic systems with zero electrical conductivity or with zero electron density. Using the technique on a prototypical 2D system, a GaAs quantum well, we uncover signatures of many-body effects involving electron-phonon interactions, plasmons, polarons, and a phonon analog of the vacuum Rabi splitting in atomic systems.
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Gupta, Anushri, Sanjeev K. Verma, Anita Kumari i B. D. Indu. "Impurity induced renormalized phonon spectrum of cuprate superconductors". International Journal of Modern Physics B 32, nr 22 (20.08.2018): 1850237. http://dx.doi.org/10.1142/s0217979218502375.
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The potential problem of anharmonic lattice vibrations in high-temperature superconductors (HTS) using the most suitable Born–Mayer–Huggins (BMH) potential has been taken up to investigate the renormalized phonon density of states (RPDOS). In order to develop the suitable results, the many body theory using quantum dynamical approach of Green’s function (GF) via an almost complete Hamiltonian (without using BCS type Hamiltonian) has been incorporated which includes harmonic electron and phonon Hamiltonian, electron–phonon interaction Hamiltonian, anharmonic and defect Hamiltonian. The derivation of anharmonic phonon GF for modified form of BMH potential enables to evaluate the renormalized and perturbed mode phonon frequencies of solids. The expressions obtained for the RPDOS can be resolved into diagonal and nondiagonal parts of which the nondiagonal part chiefly depends on impurities and disappears in pure crystals. A large number of new features are investigated in the light of this formulation followed by the numerical analysis for the energy spectrum of representative cuprate HTS YBa2Cu3O[Formula: see text]. The inclusion of defects, anharmonicities and electron–phonon interactions in the cuprate superconductors substantially modifies the scenario of RPDOS and reveals a large number of unexplained peaks in the spectrum.
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Wei, Yao, Francesco Macheda, Zelong Zhao, Terence Tse, Evgeny Plekhanov, Nicola Bonini i Cedric Weber. "High-Temperature Superconductivity in the Lanthanide Hydrides at Extreme Pressures". Applied Sciences 12, nr 2 (15.01.2022): 874. http://dx.doi.org/10.3390/app12020874.
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Hydrogen-rich superhydrides are promising high-Tc superconductors, with superconductivity experimentally observed near room temperature, as shown in recently discovered lanthanide superhydrides at very high pressures, e.g., LaH10 at 170 GPa and CeH9 at 150 GPa. Superconductivity is believed to be closely related to the high vibrational modes of the bound hydrogen ions. Here, we studied the limit of extreme pressures (above 200 GPa) where lanthanide hydrides with large hydrogen content have been reported. We focused on LaH16 and CeH16, two prototype candidates for achieving a large electronic contribution from hydrogen in the electron–phonon coupling. In this work, we propose a first-principles calculation platform with the inclusion of many-body corrections to evaluate the detailed physical properties of the Ce–H and La–H systems and to understand the structure, stability, and superconductivity of these systems at ultra-high pressure. We provide a practical approach to further investigate conventional superconductivity in hydrogen-rich superhydrides. We report that density functional theory provides accurate structure and phonon frequencies, but many-body corrections lead to an increase of the critical temperature, which is associated with the spectral weight transfer of the f-states.
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Mohanty, Vaibhav, i Eric J. Heller. "Lazy electrons in graphene". Proceedings of the National Academy of Sciences 116, nr 37 (23.08.2019): 18316–21. http://dx.doi.org/10.1073/pnas.1908624116.
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Within a tight-binding approximation, we numerically determine the time evolution of graphene electronic states in the presence of classically vibrating nuclei. There is no reliance on the Born–Oppenheimer approximation within the p-orbital tight-binding basis, although our approximation is “atomically adiabatic”: the basis p-orbitals are taken to follow nuclear positions. Our calculations show that the strict adiabatic Born–Oppenheimer approximation fails badly. We find that a diabatic (lazy electrons responding weakly to nuclear distortions) Born–Oppenheimer model provides a much more accurate picture and suggests a generalized many-body Bloch orbital-nuclear basis set for describing electron–phonon interactions in graphene.
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Zhang, Yu. "Non-Adiabatic Dynamics Simulation of Plasmon-Mediated Chemistry". ECS Meeting Abstracts MA2022-01, nr 36 (7.07.2022): 1582. http://dx.doi.org/10.1149/ma2022-01361582mtgabs.
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Localized surface plasmon resonances (LSPRs) have attracted much recent attention for their potential in promoting chemical reactions with light. However, the mechanism of LSPR-induced chemical reactions is still not clear and suffers from many controversies. This presentation will discuss the atomic-scale mechanism of plasmonic hot-carrier mediated chemical reaction exampled by H2 dissociation by employing time-dependent density functional calculations theory and non-adiabatic molecular dynamics. The key observation is that there are nested excited states corresponding to both hot-electron excitation and charge transfer [1]. These nested states cross, facilitating the transitions depicted in the desorption induced by the electronic transitions model and the surface hopping model. I believe this is the first time that such a connection has been made based on a first-principles calculation. Diabatization of these states shows that the charge transfer states are responsible for H2 dissociation, while the hot electron states do not. Previous works only identified the hot electron states, thus were unable to explain the dissociation in a convincing way. Moreover, we also found chemical reaction is tunable if the molecule is placed in the center of the plasmonic dimer [2]. The reaction rate can be either suppressed or enhanced depending on the geometry. [1] Q. Wu, L. Zhou, G. C. Schatz, Y. Zhang*, H. Guo*, J. Am. Chem. Soc. 2020, 142, 13090–13101. [2] Y. Zhang*, T. Nelson, S. Tretiak, H. Guo, G. C. Schatz. ACS Nano, 2018, 12, 8415-8422.
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Kotzott, Thomas, Mohammed Bouhassoune, Henning Prüser, Alexander Weismann, Samir Lounis i Martin Wenderoth. "Scanning tunneling spectroscopy of subsurface Ag and Ge impurities in copper". New Journal of Physics 23, nr 11 (1.11.2021): 113044. http://dx.doi.org/10.1088/1367-2630/ac3681.
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Abstract We investigate single Ge and Ag impurities buried below a Cu(100) surface using low temperature scanning tunneling microscopy. The interference patterns in the local density of states are surface scattering signatures of the bulk impurities, which result from 3D Friedel oscillations and the electron focusing effect. Comparing the isoelectronic d scatterer Ag and the sp scatterer Ge allows to distinguish contributions from impurity scattering and the host. Energy-independent effective scattering phase shifts are extracted using a plane wave tight-binding model and reveal similar values for both species. A comparison with ab initio calculations suggests incoherent sp scattering processes at the Ge impurity. As both scatterers are spectrally homogeneous, scanning tunneling spectroscopy of the interference patterns yields real-space signatures of the bulk electronic structure. We find a kink around zero bias for both species that we assign to a renormalization of the band structure due to many-body effects, which can be described with a Debye self-energy and a surprisingly high electron–phonon coupling parameter λ. We propose that this might originate from bulk propagation in the vicinity of the surface.
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CAMACHO B., A. S., i R. M. GUTIERREZ. "COHERENT DYNAMICS OF AN ASYMMETRIC DOUBLE QUANTUM WELL". Surface Review and Letters 09, nr 05n06 (październik 2002): 1623–30. http://dx.doi.org/10.1142/s0218625x02004104.
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Coherent optical effects coming from two excited levels in an engineered asymmetric double quantum well have been detected with duration of picoseconds.1 This short decoherence time is related with the dephasing time. Although dephasing is mainly due to electron–electron scattering and LO phonons in polar semiconductor provide the dominant inelastic scattering mechanism, a study of the elastic scattering with phonons during the coherent stage is also needed to understand the coherent electron dynamics. In this work is presented a microscopic study of the elastic scattering rates due to electron–LO-phonon interaction, which are obtained for each of the three conduction subbands on a tailored double asymmetric quantum well by using the imaginary part of the polaron self-energy within a many-body formalism. Both absorption and emission rates are calculated. The dephasing times for different electronic states in a given heterostructure can be very different, depending on the material, geometry, temperature, carrier density, etc. As an important geometric parameter is chosen the barrier width, which tunes the energy differences between the two upper levels or tunneling times. Electron density effect is studied through screening. Two limits are presented — unscreened and static screening. It is found that after an ultrashort pulse the absorption and emission scattering rates in each level are very different from the scattering rates in equilibrium and that screening effects can be used as coherent control mechanism.
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Wei, Zhi-Yuan, Yong Hu, Ling-Yong Zeng, Ze-Yu Li, Zhen-Hua Qiao, Hui-Xia Luo i Jun-Feng He. "Angle-resolved photoemission spectroscopy study on electronic structure of 1<i>T</i>-NbSeTe". Acta Physica Sinica 71, nr 12 (2022): 127901. http://dx.doi.org/10.7498/aps.71.20220458.
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Transition metal dichalcogenides (TMDs) have attracted a lot of interest in condensed matter physics research due to the existence of multiple novel physical phenomena, including superconductivity and charge density wave order. In this sense, TMDs also provide a uniquewindow to study the interactions between different ground states. In this paper, the electronic structure of 1<i>T</i>-NbSeTe has been systematically examined by angle-resolved photoemission spectroscopy (ARPES), for the first time. A van Hove singularity (VHS) has been identified at the <i>M</i> point, with a binding energy of 250 meV below the Fermi level. Careful analysis has been carried out to examine the band dispersion along different high symmetry directions and the possible many-body effect. However, the dispersion kink – a characteristic feature of electron-boson coupling is not obvious in this system. In TMDs materials, the van Hove singularity near the Fermi level and the electron-boson (phonon) coupling have been suggested to play an important role in the formation of charge density wave (CDW) and superconductivity, respectively. In this sense, our experimental results may provide a direct explanation for the weakened CDW and relatively low superconducting transition temperature in 1<i>T</i>-NbSeTe.Theseresults may also provide insight on the charge density wave orders in related material systems.
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Gui, Long, Jamie L. Ebner, Alexander Mileant, James A. Williams i Kelly K. Lee. "Visualization and Sequencing of Membrane Remodeling Leading to Influenza Virus Fusion". Journal of Virology 90, nr 15 (25.05.2016): 6948–62. http://dx.doi.org/10.1128/jvi.00240-16.
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ABSTRACTProtein-mediated membrane fusion is an essential step in many fundamental biological events, including enveloped virus infection. The nature of protein and membrane intermediates and the sequence of membrane remodeling during these essential processes remain poorly understood. Here we used cryo-electron tomography (cryo-ET) to image the interplay between influenza virus and vesicles with a range of lipid compositions. By following the population kinetics of membrane fusion intermediates imaged by cryo-ET, we found that membrane remodeling commenced with the hemagglutinin fusion protein spikes grappling onto the target membrane, followed by localized target membrane dimpling as local clusters of hemagglutinin started to undergo conformational refolding. The local dimples then transitioned to extended, tightly apposed contact zones where the two proximal membrane leaflets were in most cases indistinguishable from each other, suggesting significant dehydration and possible intermingling of the lipid head groups. Increasing the content of fusion-enhancing cholesterol or bis-monoacylglycerophosphate in the target membrane led to an increase in extended contact zone formation. Interestingly, hemifused intermediates were found to be extremely rare in the influenza virus fusion system studied here, most likely reflecting the instability of this state and its rapid conversion to postfusion complexes, which increased in population over time. By tracking the populations of fusion complexes over time, the architecture and sequence of membrane reorganization leading to efficient enveloped virus fusion were thus resolved.IMPORTANCEEnveloped viruses employ specialized surface proteins to mediate fusion of cellular and viral membranes that results in the formation of pores through which the viral genetic material is delivered to the cell. For influenza virus, the trimeric hemagglutinin (HA) glycoprotein spike mediates host cell attachment and membrane fusion. While structures of a subset of conformations and parts of the fusion machinery have been characterized, the nature and sequence of membrane deformations during fusion have largely eluded characterization. Building upon studies that focused on early stages of HA-mediated membrane remodeling, here cryo-electron tomography (cryo-ET) was used to image the three-dimensional organization of intact influenza virions at different stages of fusion with liposomes, leading all the way to completion of the fusion reaction. By monitoring the evolution of fusion intermediate populations over the course of acid-induced fusion, we identified the progression of membrane reorganization that leads to efficient fusion by an enveloped virus.
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Peters, William K., David E. Couch, Benoit Mignolet, Xuetao Shi, Quynh L. Nguyen, Ryan C. Fortenberry, H. Bernhard Schlegel i in. "Ultrafast 25-fs relaxation in highly excited states of methyl azide mediated by strong nonadiabatic coupling". Proceedings of the National Academy of Sciences 114, nr 52 (6.11.2017): E11072—E11081. http://dx.doi.org/10.1073/pnas.1712566114.
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Highly excited electronic states are challenging to explore experimentally and theoretically—due to the large density of states and the fact that small structural changes lead to large changes in electronic character with associated strong nonadiabatic dynamics. They can play a key role in astrophysical and ionospheric chemistry, as well as the detonation chemistry of high-energy density materials. Here, we implement ultrafast vacuum-UV (VUV)-driven electron–ion coincidence imaging spectroscopy to directly probe the reaction pathways of highly excited states of energetic molecules—in this case, methyl azide. Our data, combined with advanced theoretical simulations, show that photoexcitation of methyl azide by a 10-fs UV pulse at 8 eV drives fast structural changes and strong nonadiabatic coupling that leads to relaxation to other excited states on a surprisingly fast timescale of 25 fs. This ultrafast relaxation differs from dynamics occurring on lower excited states, where the timescale required for the wavepacket to reach a region of strong nonadiabatic coupling is typically much longer. Moreover, our theoretical calculations show that ultrafast relaxation of the wavepacket to a lower excited state occurs along one of the conical intersection seams before reaching the minimum energy conical intersection. These findings are important for understanding the unique strongly coupled non-Born–Oppenheimer molecular dynamics of VUV-excited energetic molecules. Although such observations have been predicted for many years, this study represents one of the few where such strongly coupled non-Born–Oppenheimer molecular dynamics of VUV-excited energetic molecules have been conclusively observed directly, making it possible to identify the ultrafast reaction pathways.
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Hamada, Kozo, i Katsuhiko Mikoshiba. "IP3 Receptor Plasticity Underlying Diverse Functions". Annual Review of Physiology 82, nr 1 (10.02.2020): 151–76. http://dx.doi.org/10.1146/annurev-physiol-021119-034433.
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In the body, extracellular stimuli produce inositol 1,4,5-trisphosphate (IP3), an intracellular chemical signal that binds to the IP3 receptor (IP3R) to release calcium ions (Ca2+) from the endoplasmic reticulum. In the past 40 years, the wide-ranging functions mediated by IP3R and its genetic defects causing a variety of disorders have been unveiled. Recent cryo-electron microscopy and X-ray crystallography have resolved IP3R structures and begun to integrate with concurrent functional studies, which can explicate IP3-dependent opening of Ca2+-conducting gates placed ∼90 Å away from IP3-binding sites and its regulation by Ca2+. This review highlights recent research progress on the IP3R structure and function. We also propose how protein plasticity within IP3R, which involves allosteric gating and assembly transformations accompanied by rapid and chronic structural changes, would enable it to regulate diverse functions at cellular microdomains in pathophysiological states.
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Ivády, Viktor, Krisztián Szász, Abram L. Falk, Paul V. Klimov, David J. Christle, William F. Koehl, Erik Janzén, Igor A. Abrikosov, David D. Awschalom i Ádám Gali. "Optical Nuclear Spin Polarization of Divacancies in SiC". Materials Science Forum 858 (maj 2016): 287–90. http://dx.doi.org/10.4028/www.scientific.net/msf.858.287.
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We demonstrate optically pumped dynamic nuclear polarization (DNP) of 29Si nuclear spins that are strongly coupled to paramagnetic color centers in 4H- and 6H-SiC. We observe 99%±1% degree of polarization. By combining ab initio theory with the experimental identification of the color centers’ optically excited states, we quantitatively model how the polarization derives from hyperfine-mediated level anticrossings. In addition, we developed a general model for these optical DNP processes that allows the effects of many microscopic processes to be integrated. Applying this theory, we gain a deeper insight into dynamic nuclear spin polarization. In particular, our findings show that the defect electron spin coherence times and excited state lifetimes are crucial factors in the entire DNP process. These results lay a foundation for SiC-based quantum memories, nuclear gyroscopes, and hyperpolarized probes for magnetic resonance imaging.
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Zozoulenko, I. V., i K. F. Berggren. "Quantum Transport in Open Nanostructures". VLSI Design 8, nr 1-4 (1.01.1998): 179–84. http://dx.doi.org/10.1155/1998/24813.
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Electron transport was studied in an open square quantum dot with a dimension typical for current experiments. A numerical analysis of the probability density distribution inside the dot was performed which enabled us to unambiguously map the resonant states which dominate the conductance of the structure. It was shown that, despite of the presence of dot openings, transport through the dot is effectively mediated by just a few (or even a single) eigenstates of the corresponding closed structure. In a single-mode regime in the leads, the broadening of the resonant levels is typically smaller than the mean energy level spacing, Δ. On the contrary, in the many-mode regime this broadening typically exceeds Δ and has an irregular, essentially non-Lorentzian, character. It was demonstrated that in the latter case eigenlevel spacing statistics of the corresponding closed system are not relevant to the averaged transport properties of the dot. This conclusion seems to have a number of experimental as well as numerical verifications.
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Fetzner, Susanne. "Ring-Cleaving Dioxygenases with a Cupin Fold". Applied and Environmental Microbiology 78, nr 8 (27.01.2012): 2505–14. http://dx.doi.org/10.1128/aem.07651-11.
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ABSTRACTRing-cleaving dioxygenases catalyze key reactions in the aerobic microbial degradation of aromatic compounds. Many pathways converge to catecholic intermediates, which are subject toorthoormetacleavage by intradiol or extradiol dioxygenases, respectively. However, a number of degradation pathways proceed via noncatecholic hydroxy-substituted aromatic carboxylic acids like gentisate, salicylate, 1-hydroxy-2-naphthoate, or aminohydroxybenzoates. The ring-cleaving dioxygenases active toward these compounds belong to the cupin superfamily, which is characterized by a six-stranded β-barrel fold and conserved amino acid motifs that provide the 3His or 2- or 3His-1Glu ligand environment of a divalent metal ion. Most cupin-type ring cleavage dioxygenases use an FeIIcenter for catalysis, and the proposed mechanism is very similar to that of the canonical (type I) extradiol dioxygenases. The metal ion is presumed to act as an electron conduit for single electron transfer from the metal-bound substrate anion to O2, resulting in activation of both substrates to radical species. The family of cupin-type dioxygenases also involves quercetinase (flavonol 2,4-dioxygenase), which opens up two C-C bonds of the heterocyclic ring of quercetin, a wide-spread plant flavonol. Remarkably, bacterial quercetinases are capable of using different divalent metal ions for catalysis, suggesting that the redox properties of the metal are relatively unimportant for the catalytic reaction. The major role of the active-site metal ion could be to correctly position the substrate and to stabilize transition states and intermediates rather than to mediate electron transfer. The tentative hypothesis that quercetinase catalysis involves direct electron transfer from metal-bound flavonolate to O2is supported by model chemistry.
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Hirl, P. J., i R. L. Irvine. "Reductive dechlorination of perchloroethylene using anaerobic sequencing batch biofilm reactors (AnSBBR)". Water Science and Technology 35, nr 1 (1.01.1997): 49–56. http://dx.doi.org/10.2166/wst.1997.0010.
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Chlorinated organic solvents, such as perchloroethylene (PCE) and trichloroethylene (TCE), rank in the top five of the groundwater pollutants found in the United States. During the past year, the Anaerobic Sequencing Batch Biofilm Reactor (AnSBBR) was used to select for, enrich, and modify the physiological state of one or more of the many possible microbial consortia that can participate in the reductive dechlorination of PCE. Reactors enriched on lactate or acetate were able to dechlorinate 10.5 mg (63.3 μmoles) of PCE to cis-1,2-dichloroethylene (cDCE) on a daily basis. When methanol was used as the electron donor PCE, TCE, and cDCE were detectable in the reactor at the end of a 24 hour cycle. An AnSBBR fed only H2/CO2 was able to mediate the dechlorination of PCE to TCE, cDCE, and vinyl chloride (VC). Chloride measurements provided for a reliable and accurate method for the quantification of reductive dechlorination when the sorption of the chlorinated ethylenes affected the direct measurement of these compounds.
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Skaling, Barbara, i B. M. MacKinnon. "The absorptive surfaces of Nectonema sp. (Nematomorpha: Nectonematoidea) from Pandalus montagui: histology, ultrastructure, and absorptive capabilities of the body wall and intestine". Canadian Journal of Zoology 66, nr 2 (1.02.1988): 289–95. http://dx.doi.org/10.1139/z88-043.
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The histology, ultrastructure, and absorptive capabilities of the body wall and intestine of the juvenile stages of Nectonema sp. (Nematomorpha: Nectonematoidea) that parasitize the shrimp Pandalus montagui in Passamaquoddy Bay, New Brunswick, were examined using histological, histochemical, ultrastructural, and in vitro labeling techniques. The body wall consists of a multilayered cuticle that rests on, and is produced by, a thin cellular hypodermis. The intestinal tract consists of a minute mouth, a cuticularized oesophagus, and a blind-ending intestine consisting of a lumen surrounded at different places by two, three, or four elongated cells. These cells consists of a maximum of two "absorptive" cells with microvillar luminal surfaces, and a maximum of two "secretory" cells, which contain numerous electron-dense granules. Acid and alkaline phosphatases and nonspecific esterases were detected in the outer layers of the body wall (cuticle and hypodermis) and in the intestinal cells. Such enzymes appear to be related to absorption of nutrient substances. Autoradiography experiments using [3H]leucine showed that following incubation in [3H]leucine-labeled seawater, leucine was concentrated in the hypodermis and the intestinal cells. Similar results were obtained when worms were incubated first in [3H]leucine-labeled seawater and then chased in nonlabeled L-leucine. Uptake of [3H]leucine was inhibited by L-leucine when worms were incubated in a seawater solution of [3H]leucine and excess L-leucine. In vitro absorption of [3H]leucine provides evidence that a carrier-mediated transport system operates across both the cuticle and the intestine of Nectonema sp.
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Mathers, Katherine E., i James F. Staples. "Differential posttranslational modification of mitochondrial enzymes corresponds with metabolic suppression during hibernation". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 317, nr 2 (1.08.2019): R262—R269. http://dx.doi.org/10.1152/ajpregu.00052.2019.
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During hibernation, small mammals, including the 13-lined ground squirrel ( Ictidomys tridecemlineatus), cycle between two distinct metabolic states: torpor, where metabolic rate is suppressed by >95% and body temperature falls to ~5°C, and interbout euthermia (IBE), where both metabolic rate and body temperature rapidly increase to euthermic levels. Suppression of whole animal metabolism during torpor is paralleled by rapid, reversible suppression of mitochondrial respiration. We hypothesized that these changes in mitochondrial metabolism are regulated by posttranslational modifications to mitochondrial proteins. Differential two-dimensional gel electrophoresis and two-dimensional blue-native PAGE revealed differences in the isoelectric point of several liver mitochondrial proteins between torpor and IBE. Quadrupole time-of-flight LC/MS and matrix-assisted laser desorption/ionization MS identified these as proteins involved in β-oxidation, the tricarboxylic acid cycle, reactive oxygen species detoxification, and the electron transport system (ETS). Immunoblots revealed that subunit 1 of ETS complex IV was acetylated during torpor but not IBE. Phosphoprotein staining revealed significantly greater phosphorylation of succinyl-CoA ligase and the flavoprotein subunit of ETS complex II in IBE than torpor. In addition, the 75-kDa subunit of ETS complex I was 1.5-fold more phosphorylated in torpor. In vitro treatment with alkaline phosphatase increased the maximal activity of complex I from liver mitochondria isolated from torpid, but not IBE, animals. By contrast, phosphatase treatment decreased complex II activity in IBE but not torpor. These findings suggest that the rapid changes in mitochondrial metabolism in hibernators are mediated by posttranslational modifications of key metabolic enzymes, perhaps by intramitochondrial kinases and deacetylases.
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Ramkumar, Govindaraju, Muthugoundar Subramanian Shivakumar, Mohammed Ali Alshehri, Chellasamy Panneerselvam i Samy Sayed. "Larvicidal potential of Cipadessa baccifera leaf extract-synthesized zinc nanoparticles against three major mosquito vectors". Green Processing and Synthesis 11, nr 1 (1.01.2022): 757–65. http://dx.doi.org/10.1515/gps-2022-0071.
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Abstract Mosquitoes are important vectors, which transmit many communicable diseases throughout the world. Synthetic insecticides, such as organophosphate and pyrethroids, are commonly used for their control in the vector control program. Insecticidal compounds from natural sources, notably from plants and synthesized nanoparticles (NPs) are promising tools for managing such vectors. Hence, the study aimed to analyze the insecticidal potentiality of leaf extract of Cipadessa baccifera and synthesized ZnNPs against three major mosquito vectors. The results recorded from UV-Vis spectroscopy show the peak absorption spectrum at 420 nm. In FTIR, the maximum peak value is 562.85 cm−1 assigned to the N–H group (amide group). The EDAX analysis shows a peak around 63.29, which confirms the binding intensity of selenium. In the scanning electron microscopy analysis, the synthesized ZnNPs sizes were ranging from 49.21 to 65.43 nm. The synthesized ZnNPs produced high mortality against Culex quinquefasciatus LC50 = 0.049653 mg·mL−1; LC90 = 0.9842 mg·mL−1), Anopheles stephensi (LC50 = 0.053421 mg·mL−1 and LC90 = 0.027761 mg·mL−1), and Aedes aegypti LC50 = 0.55214 mg·mL−1 and LC90 = 0.7456 mg·mL−1). These results suggest that the C. baccifera leaf extract-mediated biosynthesis of ZnNPs has the potential to be used as an ideal eco-friendly approach toward the control of mosquito vectors at early stages.
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Hajjar, Katherine A., Jia Ruan, Guangzhi Sui, Arunkumar B. Deora, Sarah Church, Leona Cohen-Gould, Shahin Rafii, David C. Lyden i Qi Ling. "Annexin 2 Mediates Plasminogen-Related Recruitment of Neovascular Mural Cells in Lymphoma Angiogenesis." Blood 110, nr 11 (16.11.2007): 3708. http://dx.doi.org/10.1182/blood.v110.11.3708.3708.
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Abstract Malignant tumor progression requires the development of tumor-associated blood vessels through co-option of nearby host vascular cells, recruitment of marrow-derived progenitor cells, or both. The annexin 2 (A2)/p11 heterotetramer is a cell surface co-receptor for the fibrinolytic proteins plasminogen (Plg) and tPA, and strongly augments the catalytic efficiency of vascular cell plasmin generation. We showed previously that A2−/ − mice display impaired postnatal angiogenesis in the corneal pocket, oxygen-induced retinopathy, and Matrigel plug assays. Here, we examined neovascularization of experimental lymphoma in mice with fibrinolytic deficiency states. For both EL4, a T cell lymphoma, and B6RV2, a B cell lymphoma, growth of implanted tumor cells was rapid in wildtype and tPA−/ − mice, but nearly flat in both A2−/ − and Plg−/ − mice. Immunohistochemical staining of EL4 tissue on day 8 revealed reduced vascular density, frequent intravascular fibrin thrombi, and dilated microvessels in A2−/ −, compared with A2+/+, mice. Electron microscopy and immunofluorescence revealed a striking paucity of pericytes and secondary dropout of endothelial cells within A2−/ − tumor microvessels. Flow cytometric analysis of circulating progenitor cells showed reduced recruitment of VEGFR1+/CD11b+ hematopoietic precursors from bone marrow to blood in A2−/ − versus A2+/+ tumor-bearing mice. In lethally irradiated A2−/ − mice, moreover, tumor growth was rescued completely upon engraftment with A2+/+ marrow. Transplantation of green fluorescent protein (GFP)-labeled A2+/+ bone marrow revealed the appearance of abundant marrow-derived CD11b+/CD68+ cells closely apposed to developing tumor neovessels. Many of these cells also express the pericyte marker, NG2. Transplantation of A2+/+ marrow, finally, restored the investment of tumor microvessels with α-smooth muscle actin-positive pericytes. These data suggest that A2 contributes critically to tumor angiogenesis in experimental lymphoma in mice, by enabling recruitment of A2+ myelomonocytic cells that promote neovascular stabilization by pericyte-like cells. The data suggest further that targeting the A2/p11 system could offer a novel strategy for the treatment of malignant lymphoma.
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Hiraishi, Masaya, Md Abdul Masum, Takashi Namba, Yuki Otani, Yaser HA Elewa, Osamu Ichii i Yasuhiro Kon. "Histopathological changes in tear-secreting tissues and cornea in a mouse model of autoimmune disease". Experimental Biology and Medicine 245, nr 12 (21.05.2020): 999–1008. http://dx.doi.org/10.1177/1535370220928275.
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The tear film covers the cornea, and its abnormalities (including immunological) induce dry eye. Using autoimmune disease model mice, BXSB/MpJ- Yaa (BXSB-Yaa), histopathological changes in the eye and tear-secreting tissues were examined using histopathology, immunohistochemistry, and electron microscopy at 8, 20, and 28 weeks for early, middle, and late disease stages. Early and middle stage BXSB-Yaa showed increased serum autoantibody and spleen weight-to-body weight (S/B) ratio, respectively, and higher tear volume than controls, BXSB/MpJ (BXSB), at early stages, which decreased with ageing and negatively correlated with autoimmune disease indices. Smaller Meibomian gland acini, intraorbital lacrimal glands, and Harderian gland acinar cells were seen in late stage BXSB-Yaa than in BXSB; the latter two indices decreased with ageing and negatively correlated with the S/B ratio. Cell infiltration occurred in the middle stage BXSB-Yaa extraorbital lacrimal gland, and acinar cells were smaller than BXSB. The conjunctival goblet cells decreased from early to middle stages in both strains, but in BXSB-Yaa, they increased at late stages with a partial lack of microvilli on the cornea and were inversely altered with anterior epithelium thickness through ageing, suggesting that they compensated for anterior epithelium damage. In conclusion, the tear film was unstable due to an autoimmune disease condition in BXSB-Yaa. Impact statement Cornea, an outermost layer of mammalian eye, is protected by tear film and abnormalities of tear film causes dry eye. Dry eye injures the cornea which results lower vision in patients. Several factors cause dry eye, including altered systemic conditions, environment, and immunological abnormality of the patient in autoimmune disease like Sjögren’s syndrome (SS). However, the detailed pathology of autoimmune abnormality-mediated dry eye is unclear. Here we demonstrated that systemic autoimmune abnormality in BXSB-Yaa mice was associated with histological changes in the exocrine glands and cornea of the eyes. We also showed that BXSB-Yaa mice developed mild or early stage dry eye-like disease and explain the existence of a compensatory mechanism associated with the dysfunction of these tissues. Thus, BXSB-Yaa could be a model for SS-like disease-associated dry eye and these data would contribute to the understanding of the pathogenesis of autoimmune-related dry eye disease.
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Zhou, Yafu, Gen Li, Guijun Han, Lulu Xun, Shaoli Mao, Luyao Yang i Yanwen Wang. "Developmental Programmed Cell Death Involved in Ontogenesis of Dictamnus dasycarpus Capitate Glandular Hairs". Plants 12, nr 2 (14.01.2023): 395. http://dx.doi.org/10.3390/plants12020395.
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Plant glandular trichomes have received much attention due to their commercial and biological value. Recent studies have focused on the development of various glands in plants, suggesting that programmed cell death (PCD) may play an important role during the development of plant secretory structures. However, the development processes and cytological characteristics in different types of plant secretory structures differed significantly. This study aims to provide new data on the developmental PCD of the capitate glandular hairs in Dictamnus dasycarpus. Light, scanning, immunofluorescence labeling, and transmission electron microscopy were used to determine the different developmental processes of the capitate glandular hairs from a cytological perspective. Morphologically, the capitate glandular hair originates from one initial epidermal cell and differentiates into a multicellular trichome characterized by two basal cells, two lines of stalk cells, and a multicellular head. It is also histochemically detected by essential oils. TUNEL-positive reactions identified nuclei with diffused fluorescence or an irregular figure by DAPI, and Evans blue staining showed that the head and stalk cells lost their viability. Ultrastructural evidence revealed the developmental process by two possible modes of PCD. Non-autolytic PCD was characterized by buckling cell walls and degenerated nuclei, mitochondria, plastids, multivesicular body (MVB), and end-expanded endoplasmic reticulum in the condensed cytoplasm, which were mainly observed in the head cells. The MVB was detected in the degraded vacuole, a degraded nucleus with condensed chromatin and diffused membrane, and eventual loss of the vacuole membrane integrity exhibited typical evidence of vacuole-mediated autolytic PCD in the stalk cells. Furthermore, protoplasm degeneration coupled with dark oil droplets and numerous micro-dark osmiophilic substances was observed during late stages. The secretion mode of essential oils is also described in this paper.
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Bachman, Ridge M., Derek M. Hall i Ljubisa R. Radovic. "A DFT Study of the VRFB Positive Electrode: Carbon Active Sites for the VO2 +/VO2+ Reaction". ECS Meeting Abstracts MA2022-01, nr 48 (7.07.2022): 2008. http://dx.doi.org/10.1149/ma2022-01482008mtgabs.
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The vanadium redox flow battery (VRFB) is a promising candidate for use in grid-scale battery applications to support a deeper reliance on intermittent renewable energy. However, it suffers from a sluggish redox reaction at the positive electrode. Previous studies indicate that its performance can be improved by oxidizing a graphene-based carbon electrode and thus increasing the concentration of its oxygen-containing surface sites. While such performance enhancement does not appear to be controversial, the underlying mechanisms is far from being clear. Some authors suggest that this procedure increases the number of electrocatalytically active sites; others simply attribute it to improved wettability. In this ongoing study, we use density functional theory (DFT) to examine the role of hydroxyl and carboxyl groups, as well as free edge carbon atoms, in the oxygen transfer process at the positive electrode. Preliminary results using carefully selected model compounds (with appropriate charge C and spin multiplicity M) indicate that oxygen functional groups are unlikely to be active sites in the electrochemical redox process, which in many respects is analogous to the oxidation reduction reaction (ORR). Both the thermodynamics (less favorable adsorption energy of vanadium oxide) and the kinetics (problematic transition states) are less plausible than in analogous mechanistic steps involving carbene-type active sites. The carbene site was probed through two possible reaction mechanisms: V-down and O-down (see graph below). The former adsorption step is essentially a ‘dead-end’ process. The latter is not only thermodynamically and kinetically more feasible; it is consistent with other oxygen-mediated electron transfer processes occurring on the surface of graphene-based materials, be they catalysts or reactants. Furthermore, it has been shown in such processes that the presence of oxygen functional groups can stabilize and enhance the concentration of free carbene-type sites at graphene edges. Figure 1
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Schäfer, Angela Maria, Martin Kemler, Robert Bauer i Dominik Begerow. "The illustrated life cycle of Microbotryum on the host plant Silene latifolia". Botany 88, nr 10 (październik 2010): 875–85. http://dx.doi.org/10.1139/b10-061.
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The plant-parasitic genus Microbotryum (Pucciniomycotina) has been used as a model for various biological studies, but fundamental aspects of its life history have not been documented in detail. The smut fungus is characterized by a dimorphic life cycle with a haploid saprophytic yeast-like stage and a dikaryotic plant-parasitic stage, which bears the teliospores as dispersal agents. In this study, seedlings and flowers of Silene latifolia Poir. (Caryophyllaceae) were inoculated with teliospores or sporidial cells of Microbotryum lychnidis-dioicae (DC. ex Liro) G. Deml & Oberw. and the germination of teliospores, the infection process, and the proliferation in the host tissue were documented in vivo using light and electron microscopy. Although germination of the teliospore is crucial for the establishment of Microbotryum, basidium development is variable under natural conditions. In flowers, where the amount of nutrients is thought to be high, the fungus propagates as sporidia, and mating of compatible cells takes place only when flowers are withering and nutrients are decreasing. On cotyledons (i.e., nutrient-depleted conditions), conjugation occurs shortly after teliospore germination, often via intrapromycelial mating. After formation of an infectious hypha with an appressorium, the invasion of the host occurs by direct penetration of the epidermis. While the growth in the plant is typically intercellular, long distance proliferation seems mediated through xylem tracheary elements. At the beginning of the vegetation period, fungal cells were found between meristematic shoot host cells, indicating a dormant phase inside the plant. By using different microscopy techniques, many life stages of Microbotryum are illustrated for the first time, thereby allowing new interpretations of laboratory data.
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Keller, Nadine, Arunasalam Naguleswaran, Angela Cannas, Nathalie Vonlaufen, Marianne Bienz, Camilla Björkman, Wolfgang Bohne i Andrew Hemphill. "Identification of a Neospora caninum Microneme Protein (NcMIC1) Which Interacts with Sulfated Host Cell Surface Glycosaminoglycans". Infection and Immunity 70, nr 6 (czerwiec 2002): 3187–98. http://dx.doi.org/10.1128/iai.70.6.3187-3198.2002.
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ABSTRACT The invasive stages of apicomplexan parasites enter their host cells through mechanisms which are largely conserved throughout the phylum. Host cell invasion is divided into two distinct events, namely, adhesion onto the host cell surface and the actual host cell entry process. The former is mediated largely through microneme proteins which are secreted at the onset of establishing contact with the host cell surface. Many of the microneme proteins identified so far contain adhesive domains. We here present the genomic and corresponding cDNA sequences coding for a 460-amino-acid (aa) microneme protein in Neospora caninum tachyzoites which, due to its homology to MIC1 in Toxoplasma gondii (TgMIC1), was named NcMIC1. The deduced NcMIC1 polypeptide sequence contains an N-terminal signal peptide of 20 aa followed by two tandemly internal repeats of 48 and 44 aa, respectively. Integrated into each repeat is a CXXXCG sequence motif reminiscent of the thrombospondin-related family of adhesive proteins. The positioning of this motif is strictly conserved in TgMIC1 and NcMIC1. The C-terminal part, comprised of 278 aa, was expressed in Escherichia coli, and antibodies affinity purified on recombinant NcMIC1 were used to confirm the localization within the micronemes by immunofluorescence and immunogold transmission electron microscopy of tachyzoites. Immunohistochemistry of mouse brains infected with tissue cysts showed that expression of this protein is reduced in the bradyzoite stage. Upon initiation of secretion by elevating the temperature to 37°C, NcMIC1 is released into the medium supernatant. NcMIC1 binds to trypsinized, rounded Vero cells, as well as to Vero cell monolayers. Removal of glycosaminoglycans from the host cell surface and modulation of host cell surface glycosaminoglycan sulfation significantly reduces the binding of NcMIC1 to the host cell surface. Solid-phase binding assays employing defined glycosaminoglycans confirmed that NcMIC1 binds to sulfated glycosaminoglycans.
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Bradner, James E., Edward F. Greenberg, Stuart L. Schreiber i Ralph Mazitschek. "Design and Characterization of a Novel, Reverse Prodrug Histone Deacetylase Inhibitor for Cutaneous T-Cell Lymphoma." Blood 108, nr 11 (16.11.2006): 4759. http://dx.doi.org/10.1182/blood.v108.11.4759.4759.
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Abstract Cutaneous T-Cell Lymphoma (CTCL) comprises a group of related lymphoproliferative disorders characterized by the presence of malignant lymphocytes in the skin. The most common variant is Mycosis Fungoides (MF), which affects approximately 500 patients per year in the United States. Though most patients with MF enjoy a normal life expectancy, they experience chronic morbidity due to the symptomatic and cosmetic manifestations of epidermotropism: erythematous patches, elevated plaques, alopecia, and cellulitis. Many patients will experience progressive disease with lymph node infiltration, tumor and a leukemic phase termed the Sezary Syndrome. The lack of a survival benefit offered by clinical trials of combination chemotherapy and radiation supports the current standard of initial topical therapy for most patients with CTCL. Topical or skin-directed approaches widely offered include: nitrogen mustards (meclorethamine or carmustine), corticosteroids, oral psoralen with UVA radiation, UVB phototherapy and electron beam irradiation. Recent, early phase clinical studies of histone deacetylase inhibitors (HDACi) have illustrated a remarkable activity among patients with advanced CTCL. The structural dissimilarity of these ligands supports an on-target antineoplastic effect. Unfortunately, the frequently severe side effects associated with the systemic delivery of these nonselective ligands may limit their downstream clinical utility in the majority of patients with this disease, even with topical administration. We therefore devised a chemical strategy to achieve high dose-intensity at the site of cutaneous disease following topical administration with limited systemic exposure. Suberohydroxamic acid phenyl ester (SHAPE) is a first-in-class reverse prodrug inhibitor of histone deacetylases. Between the aliphatic chain and aromatic capping element of this canonical HDACi, we positioned an ester bond so as to promote presystemic metabolism by serum esterases. Preclinical studies of this ligand demonstrate potent activity against nuclear and cytosolic HDAC proteins. Doses required to achieve maximal histone hyperacetylation in human cancer cell tissue culture are comparable to vorinostat (SAHA; Merck & Co., Rahway, NJ) and MS-275 (Berlex Pharmaceuticals, Montville, NJ). These studies support the stability of SHAPE in the intracellular environment amid cellular esterases. The rapid metabolism (t-½ less than 5 minutes) by serum esterases has been established biochemically using continuous spectrophotometry, and is mediated by both butyrylcholinesterase and paraoxonase. Tolerability and preliminary activity have recently been demonstrated in an IL-7 transgenic mouse model of CTCL supporting clinical development as a therapeutic strategy in humans. Application to premalignant, neoplastic and inflammatory conditions of the oropharynx is being explored. Further studies characterizing the impact of SHAPE on T-cell function are also ongoing, to assess utility in conditions such as psoriasis and cutaneous graft-versus-host disease.
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Tian, Wei, Xing Jun Li, Natalie D. Stull, Chang-Il Suh, Sergio Grinstein, MIchael B. Yaffe, Simon J. Atkinson i Mary C. Dinauer. "The Phosphoinositide-Binding Protein p40phox Regulates NADPH Oxidase Activation Rather Than Assembly during FcγIIA Receptor-Induced Phagocytosis." Blood 108, nr 11 (16.11.2006): 678. http://dx.doi.org/10.1182/blood.v108.11.678.678.
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Abstract Many critical features of the organization and regulation of the phagocyte NADPH oxidase, a complex multi-subunit enzyme that generates superoxide for microbial killing, remain poorly defined. The active enzyme includes a membrane-bound flavocytochrome b along with p47phox, p67phox, p40phox, and Rac-GTP that are present in the cytosol of resting cells. p67phox is linked by high affinity interactions with both p47phox and p40phox, which appear to translocate as a trimeric complex upon cellular activation. The p47phox subunit acts as an adaptor to promote translocation by docking at a proline-rich target sequence on the flavocytochrome, and p67phox is a Rac-GTP effector containing a domain that activates electron transport. In contrast, the function of p40phox, which is not required for high level oxidase activity in cell free systems, is poorly understood. Recently, our group showed that p40phox plays key role in the activation of superoxide production during phagocytosis of IgG-opsonized targets in COSphoxFcγR cells. This model cell line contains stable transgenes for the flavocytochrome, p47phox, p67phox, and the FcγIIA receptor, without or with an additional transgene for p40phox. p40phox-dependent coupling of FcγR-mediated phagocytosis to superoxide production required an intact p40phox PX domain, which binds to phosphatidylinositol-3-phosphate (PI3P), a phosphoinositide generated by class III PI3 kinases in phagosome membranes (Suh et al J Exp Med 203, 1915Suh et al J Exp Med 203, 2006). Furthermore, a newly developed p40phox-null mouse exhibits reduced neutrophil NADPH oxidase activity in response to selected agonists, including IgG-opsonized targets (Ellson et al J Exp Med 203, 1927Ellson et al J Exp Med 203, 2006). In the current study, we investigated whether p40phox is required for translocation of p67phox during phagocytosis. We generated COSphoxFcγR cells expressing YFP-tagged p67phox from a stable transgene instead of untagged p67phox. Following incubation with IgG-opsonized sheep red blood cells (IgG-RBC), p67phox was detected on phagosome membranes at both early stages of phagosome cup formation and after closure, independent of whether or not p40phox was also co-expressed. However, NADPH oxidase activity was not detected in IgG-RBC phagosomes in COSphoxFcγR-p67phox-YFP cells unless p40phox was present. PMA-activated superoxide production was independent of p40phox, and Western blotting indicated there was no significant difference in expression of the other oxidase subunits in COSphoxFcγR-p67phox-YFP cells without or with the p40phox transgene. Further studies in PLB-985 granulocytes expressing stable transgenes for either YFP-tagged p67phox or p40phox showed that the PI3K inhibitor wortmannin inhibited phagosome NADPH oxidase activity and translocation of p40phox, but localization of p67phox to phagosomes was unaffected. These results indicate that although p40phox positively regulates NADPH oxidase activation during phagocytosis, recruitment of p67phox to the phagosome is independent of p40phox. Taken together, these data suggest that the PX domain of p40phox acts as a PI3P-dependent switch to activate the membrane-assembled NADPH oxidase complex.
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Kinzel, Niklas Werner, Derya Demirbas, Eckhard Bill, Thomas Weyhermüller, Christophe Werlé, Nicolas Kaeffer i Walter Leitner. "Systematic Variation of 3d Metals in a Redox-Innocent Ligand Environment: Structures, Electrochemical Properties and CO2 Activation". ECS Meeting Abstracts MA2022-01, nr 49 (7.07.2022): 2078. http://dx.doi.org/10.1149/ma2022-01492078mtgabs.
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In the endeavor to close the anthropogenic carbon cycle and produce goods in a de-fossilized future, electrochemical carbon dioxide reduction constitutes a powerful tool.[1] Herein,3d transition metal complexes range among the most effective catalysts to overcome the kinetic barriers for CO2 activation.[2] In a recent literature review, we analyzed the main reaction pathways of homogeneously catalyzed CO2 electroreduction from an organometallic perspective and classified them into two mechanisms: (1) direct coordination of carbon dioxide to the metal center prior to activation and (2) formation of a metal hydride as the intermediate reactive to CO2.[3] Although properties of the metal center such as hydricity, or substrate (CO2) and product (CO, HCO2H...) binding affinity, are crucial regarding the mechanism and the ability of the complex to mediate CO2 reduction, systematic variations of the metal within an identical, redox-innocent ligand backbone remain scarcely investigated. In this study,[4] we report on the synthesis, structures, and electrochemistry of 3d transition metal complexes (M = Mn(I), Fe(II), Co(II), Ni(II), Cu(I) and Zn(II)) coordinated by a new redox-innocent PNP pincer ligand system (Figure 1). The ligand combines a large steric demand, partially shielding the metal center, with a high degree of aromaticity. With these features, the ligand only marginally interferes in the redox processes but still takes sufficient π-backbonding to stabilize low-valent metals. The coordination compounds derived thereof were analyzed by spectroscopic methods (e.g., NMR, EPR, and Mössbauer) as well as crystal X-Ray diffraction to determine their spatial and electronic structures. These findings served as the starting point for a further exploration of the electrochemical reduction of the complexes via cyclic voltammetry. While the Mn, Cu, and Zn complexes solely exhibit ligand reduction or decomposition processes, the distinct electrochemical waves found for the Fe, Co and Ni coordination compounds could be assigned to metal-centered reduction events from M(II) down to M(0). For both cobalt and nickel, the reductions appear to be accompanied by their chloride ligands being lost or exchanged with the acetonitrile solvent, a fact that we currently investigate[5] as these phenomena remain misjudged across many (CO2) electroreduction catalysts. In contrast to Co and Ni, Fe undergoes a more complex reduction pattern likely yielding a dimeric species. Despite their unequal reduction pathways, the evolution of the voltammograms of the complexes under CO2 atmosphere indicates an interaction of each of the complexes with the substrate molecule in their reduced metal states. The d10 Ni(0) species putatively forms an Aresta-type Ni-η2-CO2 complex, in which the electron transfer to the substrate through backbonding is insufficient to enable electrocatalytic activity. At contrast, CO2 binding at the d9 Co(0) intermediate likely leads to additional electron uptake and formation of a formal Co(I) metallacarboxylate complex able to promote turnover (Figure 2). Eventually, we related our findings to the few literature precedents that incorporate redox-innocent ligands. This assessment shows that beneficial characteristics in the electrochemical activation of CO2 by complexes based on redox-innocent ligands are an unsaturated coordination sphere (coordination number = 4 or 5) as well as a d7 to d9 configuration in the reduced oxidation state (+I or 0). The on-purpose design of complexes that simultaneously meet these three characteristics hence provides a promising strategy for catalyst development. In particular, dynamic structural and electronic changes under electrochemical conditions, such as the exchange of chlorido ligands with acetonitrile as faced in this study, must be controlled to ensure the primary operation of the metal centers in the desired catalytic manifold. References [1] P. De Luna, C. Hahn, D. Higgins, S. A. Jaffer, T. F. Jaramillo, E. H. Sargent, Science 2019, 364, eaav3506. [2] R. Francke, B. Schille, M. Roemelt, Chem. Rev. 2018, 118, 4631. [3] N. W. Kinzel, C. Werlé, W. Leitner, Angew. Chem. Int. Ed. 2021, 60, 11628. [4] N. W. Kinzel,D. Demirbas, E. Bill, T. Weyhermüller, C. Werlé,N. Kaeffer, W. Leitner, Inorg. Chem. 2021, doi: 10.1021/acs.inorgchem.1c02909. [5] N. W. Kinzel, N. Kaeffer, W. Leitner in preparation. Figure 1
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Wang, Wenqing, Andrew Devilbiss, Thomas Mathews, Martin Arreola, Misty Martin, Zhiyu Zhao, Avni Awani i in. "Reticular Dysgenesis-Associated Adenylate Kinase 2 Deficiency Impairs Hematopoietic Stem and Progenitor Cell Function through Reductive Stress". Blood 136, Supplement 1 (5.11.2020): 33. http://dx.doi.org/10.1182/blood-2020-138560.
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Energy deficiency and redox stress are hallmarks of mitochondrial pathology. Reductive stress is marked by an accumulation of reducing species and can arise from defects in the electron transport chain (ETC) that prevent NAD+ regeneration from NADH. Reticular Dysgenesis (RD) is a particularly grave form of severe combined immunodeficiency (SCID), characterized by maturation arrest of both myeloid and lymphoid lineages. Unlike other forms of SCID, RD is a mitochondriopathy caused by biallelic mutations in the mitochondrial enzyme adenylate kinase 2 (AK2). AK2 catalyzes the phosphorylation of adenosine monophosphate (AMP) to adenosine diphosphate (ADP), and maintains ADP availability for ATP synthase. We hypothesize that AK2 deficiency leads to decreased ETC activities and defective NAD+ regeneration. Emerging evidence suggests that the development of hematopoietic stem and progenitor cells (HSPCs) is intricately intertwined with various aspects of mitochondrial function. Investigating the cellular and molecular consequences of AK2 deficiency during myelopoiesis provides fundamental insight into the pathology of many mitochondrial disorders. Methods: To recapitulate RD myeloid maturation defects, we developed an AK2 biallelic knock out model in human HSPCs using CRISPR gene editing. HSPCs were edited at the AK2 locus, and cells with biallelic AK2 knock out were enriched using homologous recombination-mediated dual reporters. HSPCs edited at the safe harbor locus AAVS1 were used as a control. When differentiated along the myeloid lineage in vitro, AK2-/- HSPCs showed significantly decreased proliferation, lower commitment to the granulocytic lineage, and maturation arrest at the promyelocyte stage, mimicking the presentation of RD patients. To dissect differentiation stage specific changes in metabolism, metabolomics analysis (LC-MS/MS), metabolic flux analysis (Seahorse assays) and RNA-seq were performed on FACS sorted populations of promyelocytes (PMs), metamyelocytes (MCs) and neutrophils (NPs). Additionally, mitochondrial membrane potential and ribosomal RNA (rRNA) content were quantified using TMRM and pyronin Y staining. Results: AK2-/- MCs and NPs showed higher AMP levels, and increased AMP/ADP and AMP/ATP ratios, in line with AK2's function to regenerate ADP from AMP. Mitochondrial oxygen consumption rate decreased, and mitochondrial membrane potential increased in AK2-/- MCs and NPs, indicating defective ETC function and ATP synthesis. Consistent with these results, TCA cycle metabolites were downregulated while pathways that fuel the TCA cycle, i.e. glycolysis and fatty acid oxidation, were upregulated. Interestingly, we observed a significant decrease in NAD+ levels, and an increase in NADH/NAD+ and GSH/GSSG ratios in AK2-/- MCs and NPs, indicative of reductive stress. These results suggest that AK2 deficiency compromises mitochondrial respiration, leading to NAD+ depletion and reductive stress in later stages of myeloid development. Defective mitochondrial respiration has been shown to impair NAD+-dependent aspartate and purine biosynthesis. In AK2-/- MCs and NPs, we observed a profound aspartate depletion and build-up of the purine precursor inosine monophosphate (IMP). As a building block for DNA and RNA, purine deficiency is known to block cell proliferation. Genes in cell cycle and ribosomal biogenesis pathways were down regulated in AK2-/- MCs and NPs. In addition, rRNA content was significantly decreased. These data raise the possibility that purine deficiency in AK2-/- HSPCs compromises nucleotide/protein synthesis along with cell cycle progression. Conclusions: Using an AK2 biallelic knock out HSPC model for RD, we have shown that defective mitochondrial respiration in AK2-/- HSPCs leads to reductive stress, NAD+ and purine depletion resulting in compromised nucleotide/protein synthesis and impaired cell cycle progression. Notably, these defects worsen as myeloid maturation progresses, possibly reflecting the increasing mitochondrial metabolic demand. We are currently exploring whether correcting the NADH/NAD+ ratio in AK2-/- HSPCs improves purine synthesis and restores myelopoiesis. Understanding how redox metabolism governs HSPC differentiation will not only allow us to delineate metabolic changes during development, but enable us to develop novel therapies for RD and other mitochondrial disorders. Disclosures Dever: Integral Medicines: Current Employment.
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Lewandowski, Cyprian, Stevan Nadj-Perge i Debanjan Chowdhury. "Does filling-dependent band renormalization aid pairing in twisted bilayer graphene?" npj Quantum Materials 6, nr 1 (30.09.2021). http://dx.doi.org/10.1038/s41535-021-00379-6.
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AbstractMagic-angle twisted bilayer graphene (MATBG) exhibits a panoply of many-body phenomena that are intimately tied to the appearance of narrow and well-isolated electronic bands. The microscopic ingredients that are responsible for the complex experimental phenomenology include electron–electron (phonon) interactions and nontrivial Bloch wavefunctions associated with the narrow bands. Inspired by recent experiments, we focus on two independent quantities that are considerably modified by Coulomb interaction-driven band renormalization, namely the density of states and the minimal spatial extent associated with the Wannier functions. First, we show that a filling-dependent enhancement of the density of states, caused by band flattening, in combination with phonon-mediated attraction due to electron-phonon umklapp processes, increases the tendency towards superconducting pairing in a range of angles around magic-angle. Second, we demonstrate that the minimal spatial extent associated with the Wannier functions, which contributes towards increasing the superconducting phase stiffness, also develops a nontrivial enhancement due to the interaction-induced renormalization of the Bloch wavefunctions. While our modeling of superconductivity (SC) assumes a weak electron-phonon coupling and does not consider many of the likely relevant correlation effects, it explains simply the experimentally observed robustness of SC in the wide range of angles that occurs in the relevant range of fillings.
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Adhikary, Priyo, i Tanmoy Das. "Novel attractive pairing interaction in strongly correlated superconductors". SciPost Physics 7, nr 6 (9.12.2019). http://dx.doi.org/10.21468/scipostphys.7.6.078.
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Conventional and unconventional superconductivity, respectively, arise from attractive (electron-phonon) and repulsive (many-body Coulomb) interactions with fixed-sign and sign-reversal pairing symmetries. Although heavy-fermions, cuprates, and pnictides are widely believed to be unconventional superconductors, recent evidence in one of the heavy fermion superconductor (CeCu_22Si_22) indicate the presence of a novel conventional type pairing symmetry beyond the electron-phonon coupling. We present a new mechanism of attractive potential between electrons, mediated by emergent boson fields (vacuum or holon) in the strongly correlated mixed valence compounds. In the strong coupling limit, localized electron sites are protected from double occupancy, which results in an emergent holon fields. The holon states can, however, attract conduction electrons through valence fluctuation channel, and the resulting doubly occupied states with local and conduction electrons condenseas Cooper pairs with onsite, fixed-sign, s-wave pairing symmetry. We develop the corresponding self-consistent theory of superconductivity, and compare the results with experiments. Our theory provides a new mechanism of superconductivity whose applicability extends to the wider class of intermetallic/mixed-valence materials and other flat-band metals.
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Patton, Kelly R. "Interaction mediated electron transport within the many-body tunnelling Hamiltonian". Physica Scripta, 17.05.2023. http://dx.doi.org/10.1088/1402-4896/acd667.
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Abstract For a non-superconducting system and in the spirit of the transfer or tunnelling Hamiltonian formalism, an expression for the electronic tunnelling current through an insulating barrier is calculated, explicitly taking into account the effects of electron-electron interactions that can persist across the barrier. In the presence of a single tunnelling barrier, the exact Hamiltonian is projected onto the subspaces of the “left” and “right” conducting leads. In the weak-tunnelling limit, the well- known tunnelling Hamiltonian is recovered, along with an additional term. This additional term originates from the projection of the electron-electron interaction onto each subspace and corresponds to a correlated or interaction-mediated tunnelling. It is shown that the tunnelling current in this approximation is related to—in addition to the single-particle density of states—the two-particle spin-spin and density-density susceptibilities. The signatures of these terms have been observed in scanning tunnelling microscope experiments on atomic spin chains.
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Belvin, Carina A., Edoardo Baldini, Ilkem Ozge Ozel, Dan Mao, Hoi Chun Po, Clifford J. Allington, Suhan Son i in. "Exciton-driven antiferromagnetic metal in a correlated van der Waals insulator". Nature Communications 12, nr 1 (10.08.2021). http://dx.doi.org/10.1038/s41467-021-25164-8.
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AbstractCollective excitations of bound electron-hole pairs—known as excitons—are ubiquitous in condensed matter, emerging in systems as diverse as band semiconductors, molecular crystals, and proteins. Recently, their existence in strongly correlated electron materials has attracted increasing interest due to the excitons’ unique coupling to spin and orbital degrees of freedom. The non-equilibrium driving of such dressed quasiparticles offers a promising platform for realizing unconventional many-body phenomena and phases beyond thermodynamic equilibrium. Here, we achieve this in the van der Waals correlated insulator NiPS3 by photoexciting its newly discovered spin–orbit-entangled excitons that arise from Zhang-Rice states. By monitoring the time evolution of the terahertz conductivity, we observe the coexistence of itinerant carriers produced by exciton dissociation and a long-wavelength antiferromagnetic magnon that coherently precesses in time. These results demonstrate the emergence of a transient metallic state that preserves long-range antiferromagnetism, a phase that cannot be reached by simply tuning the temperature. More broadly, our findings open an avenue toward the exciton-mediated optical manipulation of magnetism.
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Mareev, Evgenii, i Fedor Potemkin. "Dynamics of ultrafast phase transitions in MgF2 triggered by laser-induced THz coherent phonons". Scientific Reports 12, nr 1 (22.04.2022). http://dx.doi.org/10.1038/s41598-022-09815-4.
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AbstractThe advent of free-electron lasers opens new routes for experimental high-pressure physics, which allows studying dynamics of condensed matter with femtosecond resolution. A rapid compression, that can be caused by laser-induced shock impact, leads to the cascade of high-pressure phase transitions. Despite many decades of study, a complete understanding of the lattice response to such a compression remains elusive. Moreover, in the dynamical case (in contrast to quasi-static loading) the thresholds of phase transitions can change significantly. Using the third harmonic pump–probe technique combined with molecular dynamics to simulate the terahertz (THz) spectrum, we revealed the dynamics of ultrafast laser-induced phase transitions in MgF2 in all-optical experiment. Tight focusing of femtosecond laser pulse into the transparent medium leads to the generation of sub-TPa shock waves and THz coherent phonons. The laser-induced shock wave propagation drastically displaces atoms in the lattice, which leads to phase transitions. We registered a cascade of ultrafast laser-induced phase transitions (P42/mnm ⇒ Pa-3 ⇒ Pnam) in magnesium fluoride as a change in the spectrum of coherent phonons. The phase transition has the characteristic time of 5–10 ps, and the lifetime of each phase is on the order of 40–60 ps. In addition, phonon density of states, simulated by molecular dynamics, together with third-harmonic time-resolved spectra prove that laser-excited phonons in a bulk of dielectrics are generated by displacive excitation (DECP) mechanism in plasma mediated conditions.
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Zhou, Ling, Junwei Huang, Lukas Windgaetter, Chin Shen Ong, Xiaoxu Zhao, Caorong Zhang, Ming Tang i in. "Unconventional excitonic states with phonon sidebands in layered silicon diphosphide". Nature Materials, 16.06.2022. http://dx.doi.org/10.1038/s41563-022-01285-3.
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AbstractComplex correlated states emerging from many-body interactions between quasiparticles (electrons, excitons and phonons) are at the core of condensed matter physics and material science. In low-dimensional materials, quantum confinement affects the electronic, and subsequently, optical properties for these correlated states. Here, by combining photoluminescence, optical reflection measurements and ab initio theoretical calculations, we demonstrate an unconventional excitonic state and its bound phonon sideband in layered silicon diphosphide (SiP2), where the bound electron–hole pair is composed of electrons confined within one-dimensional phosphorus–phosphorus chains and holes extended in two-dimensional SiP2 layers. The excitonic state and emergent phonon sideband show linear dichroism and large energy redshifts with increasing temperature. Our ab initio many-body calculations confirm that the observed phonon sideband results from the correlated interaction between excitons and optical phonons. With these results, we propose layered SiP2 as a platform for the study of excitonic physics and many-particle effects.
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Hader, Joerg, Josefine Neuhaus, Jerome V. Moloney i Stephan W. Koch. "On the importance of electron-electron and electron-phonon scatterings and energy renormalizations during carrier relaxation in monolayer transition-metal dichalcogenides". Journal of Physics: Condensed Matter, 22.04.2022. http://dx.doi.org/10.1088/1361-648x/ac699e.
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Abstract An ab initio based fully microscopic many-body approach is used to study the carrier relaxation dynamics in monolayer transition-metal dichalcogenides. Bandstructures and wavefunctions as well as phonon energies and coupling matrix elements are calculated using density functional theory. The resulting dipole and Coulomb matrix elements are implemented in the Dirac-Bloch equations to calculate carrier-carrier and carrier-phonon scatterings throughout the whole Brillouin zone. It is shown that carrier scatterings lead to a relaxation into hot quasi-Fermi distributions on a single femtosecond timescale. Carrier cool down and inter-valley transitions are mediated by phonon scatterings on a picosecond timescale. Strong, density-dependent energy renormalizations are shown to be valley-dependent. For MoTe2, MoSe2 and MoS2 the change of energies with occupation is found to be about 50% stronger in the Σ and λ side valleys than in the K and K' valleys. However, for realistic carrier densities, the materials always maintain their direct bandgap at the K points of the Brillouin zone.
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Walczak, Kamil. "Decoherence in elastic and polaronic transport via discrete quantum states". Open Physics 4, nr 2 (1.01.2006). http://dx.doi.org/10.2478/s11534-006-0009-y.
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AbstractIn this work we study the effect of decoherence on elastic and polaronic transport via discrete quantum states. Calculations are performed with the help of a nonperturbative computational scheme, based on Green’s function theory within the framework of polaron transformation (GFT-PT), where the many-body electron-phonon interaction problem is mapped exactly into a single-electron multi-channel scattering problem. In particular, the influence of dephasing and relaxation processes on the shape of the electrical current and shot noise curves is discussed in detail under linear and nonlinear transport conditions.
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Magoni, Matteo, Paolo Mazza i Igor Lesanovsky. "Phonon dressing of a facilitated one-dimensional Rydberg lattice gas". SciPost Physics Core 5, nr 3 (23.08.2022). http://dx.doi.org/10.21468/scipostphyscore.5.3.041.
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We study the dynamics of a one-dimensional Rydberg lattice gas under facilitation (anti-blockade) conditions which implements a so-called kinetically constrained spin system. Here an atom can only be excited to a Rydberg state when one of its neighbors is already excited. Once two or more atoms are simultaneously excited mechanical forces emerge, which couple the internal electronic dynamics of this many-body system to external vibrational degrees of freedom in the lattice. This electron-phonon coupling results in a so-called phonon dressing of many-body states which in turn impacts on the facilitation dynamics. In our theoretical study we focus on a scenario in which all energy scales are sufficiently separated such that a perturbative treatment of the coupling between electronic and vibrational states is possible. This allows to analytically derive an effective Hamiltonian for the evolution of clusters of consecutive Rydberg excitations in the presence of phonon dressing. We analyze the spectrum of this Hamiltonian and show --- by employing Fano resonance theory --- that the interaction between Rydberg excitations and lattice vibrations leads to the emergence of slowly decaying bound states that inhibit fast relaxation of certain initial states.
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Merkl, Philipp, Chaw-Keong Yong, Marlene Liebich, Isabella Hofmeister, Gunnar Berghäuser, Ermin Malic i Rupert Huber. "Proximity control of interlayer exciton-phonon hybridization in van der Waals heterostructures". Nature Communications 12, nr 1 (19.03.2021). http://dx.doi.org/10.1038/s41467-021-21780-6.
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AbstractVan der Waals stacking has provided unprecedented flexibility in shaping many-body interactions by controlling electronic quantum confinement and orbital overlap. Theory has predicted that also electron-phonon coupling critically influences the quantum ground state of low-dimensional systems. Here we introduce proximity-controlled strong-coupling between Coulomb correlations and lattice dynamics in neighbouring van der Waals materials, creating new electrically neutral hybrid eigenmodes. Specifically, we explore how the internal orbital 1s-2p transition of Coulomb-bound electron-hole pairs in monolayer tungsten diselenide resonantly hybridizes with lattice vibrations of a polar capping layer of gypsum, giving rise to exciton-phonon mixed eigenmodes, called excitonic Lyman polarons. Tuning orbital exciton resonances across the vibrational resonances, we observe distinct anticrossing and polarons with adjustable exciton and phonon compositions. Such proximity-induced hybridization can be further controlled by quantum designing the spatial wavefunction overlap of excitons and phonons, providing a promising new strategy to engineer novel ground states of two-dimensional systems.
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Kounalakis, Marios, Yaroslav M. Blanter i Gary A. Steele. "Synthesizing multi-phonon quantum superposition states using flux-mediated three-body interactions with superconducting qubits". npj Quantum Information 5, nr 1 (21.11.2019). http://dx.doi.org/10.1038/s41534-019-0219-y.
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AbstractMassive mechanical resonators operating at the quantum scale can enable a large variety of applications in quantum technologies as well as fundamental tests of quantum theory. Of crucial importance in that direction is both their integrability into state-of-the-art quantum platforms as well as the ability to prepare them in generic quantum states using well-controlled high-fidelity operations. Here, we propose a scheme for controlling a radio-frequency mechanical resonator at the quantum scale using two superconducting transmon qubits that can be integrated on the same chip. Specifically, we consider two qubits coupled via a capacitor in parallel to a superconducting quantum interference device (SQUID), which has a suspended mechanical beam embedded in one of its arms. Following a theoretical analysis of the quantum system, we find that this configuration, in combination with an in-plane magnetic field, can give rise to a tuneable three-body interaction in the single-photon strong-coupling regime, while enabling suppression of the stray qubit-qubit coupling. Using state-of-the-art parameters and qubit operations at single-excitation levels, we numerically demonstrate the possibility of ground-state cooling as well as high-fidelity preparation of mechanical quantum states and qubit-phonon entanglement, i.e. states having negative Wigner functions and obeying non-classical correlations. Our work significantly extends the quantum control toolbox of radio-frequency mechanical resonators and may serve as a promising architecture for integrating such mechanical elements with transmon-based quantum processors.
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Aggoune, Wahib, Alberto Eljarrat, Dmitrii Nabok, Klaus Irmscher, Martina Zupancic, Zbigniew Galazka, Martin Albrecht, Christoph Koch i Claudia Draxl. "A consistent picture of excitations in cubic BaSnO3 revealed by combining theory and experiment". Communications Materials 3, nr 1 (3.03.2022). http://dx.doi.org/10.1038/s43246-022-00234-6.
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AbstractAmong the transparent conducting oxides, the perovskite barium stannate is most promising for various electronic applications due to its outstanding carrier mobility achieved at room temperature. However, most of its important characteristics, such as band gaps, effective masses, and absorption edge, remain controversial. Here, we provide a fully consistent picture by combining state-of-the-art ab initio methodology with forefront electron energy-loss spectroscopy and optical absorption measurements. Valence electron energy-loss spectra, featuring signals originating from band gap transitions, are acquired on defect-free sample regions of a BaSnO3 single crystal. These high-energy-resolution measurements are able to capture also very weak excitations below the optical gap, attributed to indirect transitions. By temperature-dependent optical absorption measurements, we assess band-gap renormalization effects induced by electron-phonon coupling. Overall, we find for the effective electronic mass, the direct and the indirect gap, the optical gap, as well as the absorption onsets and spectra, excellent agreement between both experimental techniques and the theoretical many-body results, supporting also the picture of a phonon-mediated mechanism where indirect transitions are activated by phonon-induced symmetry lowering. This work demonstrates a fruitful connection between different high-level theoretical and experimental methods for exploring the characteristics of advanced materials.
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Lin, Kai-Qiang, Chin Shen Ong, Sebastian Bange, Paulo E. Faria Junior, Bo Peng, Jonas D. Ziegler, Jonas Zipfel i in. "Narrow-band high-lying excitons with negative-mass electrons in monolayer WSe2". Nature Communications 12, nr 1 (17.09.2021). http://dx.doi.org/10.1038/s41467-021-25499-2.
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AbstractMonolayer transition-metal dichalcogenides (TMDCs) show a wealth of exciton physics. Here, we report the existence of a new excitonic species, the high-lying exciton (HX), in single-layer WSe2 with an energy of ~3.4 eV, almost twice the band-edge A-exciton energy, with a linewidth as narrow as 5.8 meV. The HX is populated through momentum-selective optical excitation in the K-valleys and is identified in upconverted photoluminescence (UPL) in the UV spectral region. Strong electron-phonon coupling results in a cascaded phonon progression with equidistant peaks in the luminescence spectrum, resolvable to ninth order. Ab initio GW-BSE calculations with full electron-hole correlations explain HX formation and unmask the admixture of upper conduction-band states to this complex many-body excitation. These calculations suggest that the HX is comprised of electrons of negative mass. The coincidence of such high-lying excitonic species at around twice the energy of band-edge excitons rationalizes the excitonic quantum-interference phenomenon recently discovered in optical second-harmonic generation (SHG) and explains the efficient Auger-like annihilation of band-edge excitons.
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Cai, Min, Mao-Peng Miao, Yunfan Liang, Zeyu Jiang, Zhen-Yu Liu, Wen-Hao Zhang, Xin Liao i in. "Manipulating single excess electrons in monolayer transition metal dihalide". Nature Communications 14, nr 1 (21.06.2023). http://dx.doi.org/10.1038/s41467-023-39360-1.
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AbstractPolarons are entities of excess electrons dressed with local response of lattices, whose atomic-scale characterization is essential for understanding the many body physics arising from the electron-lattice entanglement, yet difficult to achieve. Here, using scanning tunneling microscopy and spectroscopy (STM/STS), we show the visualization and manipulation of single polarons in monolayer CoCl2, that are grown on HOPG substrate via molecular beam epitaxy. Two types of polarons are identified, both inducing upward local band bending, but exhibiting distinct appearances, lattice occupations and polaronic states. First principles calculations unveil origin of polarons that are stabilized by cooperative electron-electron and electron-phonon interactions. Both types of polarons can be created, moved, erased, and moreover interconverted individually by the STM tip, as driven by tip electric field and inelastic electron tunneling effect. This finding identifies the rich category of polarons in CoCl2 and their feasibility of precise control unprecedently, which can be generalized to other transition metal halides.
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Qu, Dai-Wei, Bin-Bin Chen, Hong-Chen Jiang, Yao Wang i Wei Li. "Spin-triplet pairing induced by near-neighbor attraction in the extended Hubbard model for cuprate chain". Communications Physics 5, nr 1 (21.10.2022). http://dx.doi.org/10.1038/s42005-022-01030-x.
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AbstractIn quantum materials, the electronic interaction and the electron-phonon coupling are, in general, two essential ingredients, the combined impact of which may drive exotic phases. Recently, an anomalously strong electron-electron attraction, likely mediated by phonons, has been proposed in one-dimensional copper-oxide chain Ba2−xSrxCuO3+δ. Yet, it is unclear how this strong near-neighbor attraction V influences the superconductivity pairing in the system. Here we perform accurate many-body calculations to study the extended Hubbard model with on-site Coulomb repulsion U > 0 and near-neighbor attraction V < 0 that could well describe the cuprate chain and likely other similar transition-metal materials with both strong correlations and lattice effects. We find a rich quantum phase diagram containing an intriguing Tomonaga-Luttinger liquid phase — besides the spin density wave and various phase separation phases — that can host dominant spin-triplet pairing correlations and divergent superconductive susceptibility. Upon doping, the spin-triplet superconducting regime can be further broadened, offering a feasible mechanism to realize p-wave superconductivity in realistic cuprate chains.