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DYAKONOV, M. I. "SPIN HALL EFFECT". International Journal of Modern Physics B 23, nr 12n13 (20.05.2009): 2556–65. http://dx.doi.org/10.1142/s0217979209061986.
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A review of the phenomenology of the Spin Hall Effect and related phenomena originating from the coupling between spin and charge currents by spin-orbit interaction is presented. The physical origin of various effects in spin-dependent scattering is demonstrated. A previously unknown feature of spin transport, the swapping of spin currents, is discussed.
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Zhang, Yun-Hai, i Ming-Hua Zhang. "Hall and Nernst effects in monolayer MoS2". International Journal of Modern Physics B 30, nr 08 (30.03.2016): 1650041. http://dx.doi.org/10.1142/s0217979216500417.
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We study Hall and Nernst transports in monolayer MoS2based on Green’s function formalism. We have derived analytical results for spin and valley Hall conductivities in the zero temperature and spin and valley Nernst conductivities in the low temperature. We found that tuning of the band gap and spin-orbit splitting can drive system transition from spin Hall insulator (SHI) to valley Hall insulator (VHI). When the system is subjected to a temperature gradient, the spin and valley Nernst conductivities are dependent on Berry curvature.
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GANICHEV, S. D. "MAGNETO-GYROTROPIC PHOTOGALVANIC EFFECTS IN SEMICONDUCTOR QUANTUM WELLS". International Journal of Modern Physics B 22, nr 01n02 (20.01.2008): 115–16. http://dx.doi.org/10.1142/s0217979208046189.
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The spin-orbit coupling provides a versatile tool to generate and to manipulate the spin degree of freedom in low-dimensional semiconductor structures. The spin Hall effect, where an electric current drives a transverse spin current and causes a nonequilibrium spin accumulation near the sample boundary,1,2 the spin-galvanic effect, where a nonequilibrium spin polarization drives an electric current3,4 or the reverse process, in which an electrical current generates a non-equilibrium spin-polarization,5–9 are all consequences of spin-orbit coupling. In order to observe a spin Hall effect a bias driven current is an essential prerequisite. Then spin separation is caused via spin-orbit coupling either by Mott scattering (extrinsic spin Hall effect) or by spin splitting of the band structure (intrinsic spin Hall effect). Recently an elementary effect causing spin separation which is fundamentally different from that of the spin Hall effect has been observed.10 In contrast to the spin Hall effect it does not require an electric current to flow: it is spin separation achieved by spin-dependent scattering of electrons in media with suitable symmetry. It is show that by free carrier (Drude) absorption of terahertz radiation spin separation is achieved in a wide range of temperatures from liquid helium temperature up to room temperature. Moreover the experimental results demonstrate that simple electron gas heating by any means is already sufficient to yield spin separation due to spin-dependent energy relaxation processes of non-equilibrium carriers. In order to demonstrate the existence of the spin separation due to asymmetric scattering the pure spin current was converted into an electric current. It is achieved by application of a magnetic field which polarizes spins. This is analogues to spin-dependent scattering in transport experiments: spin-dependent scattering in an unpolarized electron gas causes the extrinsic spin Hall effect, whereas in a spin-polarized electron gas a charge current, the anomalous Hall effect, can be observed. As both magnetic fields and gyrotropic mechanisms were used authors introduced the notation "magneto-gyrotropic photogalvanic effects" for this class of phenomena. The effect is observed in GaAs and InAs low dimensional structures at free-carrier absorption of terahertz radiation in a wide range of temperatures from liquid helium temperature up to room temperature. The results are well described by the phenomenological description based on the symmetry. Experimental and theoretical analysis evidences unumbiguously that the observed photocurrents are spin-dependent. Microscopic theory of this effect based on asymmetry of photoexcitation and relaxation processes are developed being in a good agreement with experimental data. Note from Publisher: This article contains the abstract only.
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Ezawa, Motohiko. "Spin-dependent Coulomb interaction and quantum Hall effects in graphene". Physica B: Condensed Matter 403, nr 5-9 (kwiecień 2008): 1502–4. http://dx.doi.org/10.1016/j.physb.2007.10.193.
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Soukhorukov, Andrey V., Davud V. Guseinov, Alexei V. Kudrin, Sergey A. Popkov, Alexandra P. Detochenko, Alexandra V. Koroleva, Alexander A. Ezhevskii, Anton A. Konakov, Nikolai V. Abrosimov i Helge Riemann. "The Impurity Spin-Dependent Scattering Effects in the Transport and Spin Resonance of Conduction Electrons in Bismuth Doped Silicon". Solid State Phenomena 242 (październik 2015): 327–31. http://dx.doi.org/10.4028/www.scientific.net/ssp.242.327.
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Transport and spin relaxation characteristics of the conduction electrons in silicon samples doped with bismuth in the 1.1·1013- 7.7·1015cm-3concentration range were studied by the Hall and electron spin resonance spectroscopy. Hall effect measurements in the temperature range 10-80 K showed a deviation from the linear dependence of the Hall resistance in the magnetic field, which is a manifestation of the anomalous Hall effect. The magnetoresistance investigation shows that with current increasing magnetoresistance may change its sign from positive to negative, which is most clearly seen when the bismuth concentration goes up to 7.7·1015cm-3. The conduction electron spin relaxation rate dramatically increases in silicon samples with sufficiently low concentration of bismuth ~ 2·1014cm-3. All these results can be explained in terms of the concept of spin-dependent and spin flip scattering induced by heavy bismuth impurity centers.
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Shah, Muzamil. "Probing topological quantum phase transitions via photonic spin Hall effects in spin-orbit coupled 2D quantum materials". Journal of Physics D: Applied Physics 55, nr 10 (6.12.2021): 105105. http://dx.doi.org/10.1088/1361-6463/ac3c76.
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Abstract Topological photonics is an emerging field in photonics in which various topological and geometrical ideas are used to manipulate and control the behavior of light photons. The interplay between topological matter and the spin degree of freedom of photons provides new opportunities for achieving spin-based photonics applications. In this paper, the photonic spin Hall effect (PSHE) of reflected light from the surface of the topological silicene quantum systems subjected to external electric and radiation fields in the terahertz regime is theoretically investigated. By tuning the external electric and the applied laser fields, we can drive the silicenic system through different topological quantum phase transitions. We demonstrate that the in-plane and transverse spatial spin dependent shifts exhibit extreme values near Brewster’s angles and away from the optical transition frequencies. We reveal that the photonic spin Hall shifts are sensitive to the spin and valley indices as well as to the number of closed gaps. We believe that the spin and valley-resolved PSHE will greatly impact the research in spinoptics, spintronics, and valleytronics.
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Bagraev, N. T., L. E. Klyachkin, V. S. Khromov, A. M. Malyarenko, V. A. Mashkov, T. V. Matveev, V. V. Romanov, N. I. Rul i K. B. Taranets. "High Temperature Quantum Kinetic Effects in Silicon Nanosandwiches". Физика и техника полупроводников 52, nr 4 (2018): 473. http://dx.doi.org/10.21883/ftp.2018.04.45822.11.
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AbstractThe negative- U impurity stripes confining the edge channels of semiconductor quantum wells are shown to allow the effective cooling inside in the process of the spin-dependent transport, with the reduction of the electron-electron interaction. The aforesaid promotes also the creation of composite bosons and fermions by the capture of single magnetic flux quanta on the edge channels under the conditions of low sheet density of carriers, thus opening new opportunities for the registration of the high temperature de Haas-van Alphen, 300 K, quantum Hall, 77 K, effects as well as quantum conductance staircase in the silicon sandwich structure.
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Bajracharya, Prabesh, Vinay Sharma, Anthony Johnson i Ramesh C. Budhani. "Resonant precession of magnetization and precession—induced DC voltages in FeGaB thin films". Journal of Physics D: Applied Physics 55, nr 7 (12.11.2021): 075303. http://dx.doi.org/10.1088/1361-6463/ac34ab.
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Abstract Measurements of frequency dependent ferromagnetic resonance and spin pumping driven dc voltage (V dc) are reported for amorphous films of Fe78Ga13B9 alloy to address the phenomenon of self-induced inverse spin Hall effect (ISHE) in plain films of metallic ferromagnets (FMs). The V dc signal, which is anti-symmetric on field reversal, comprises of symmetric and asymmetric Lorentzians centered around the resonance field. Dominant role of thin film size effects is seen in setting the magnitude of static magnetization, V dc and dynamics of magnetization precession in thinner films (⩽8 nm). The film thickness dependence of magnetization parameters indicates the presence of a magnetically disordered region at the film—substrate interface, which may promote preferential flow of spins generated by the precessing magnetization towards the substrate. However, the V dc signal also draws contributions from rectification effects of a ≈0.4% anisotropic magnetoresistance and a large (≈54 nΩ m) anomalous Hall resistivity (AHR) of these films which ride over the effect of spin–orbit coupling driven spin-to-charge conversion near the film—substrate interface. We have addressed these data in the framework of the existing theories of electrodynamics of a ferromagnetic film subjected to radio-frequency field in a coplanar waveguide geometry. Our estimation of the self-induced ISHE for the sample with 54 nΩ m AHR shows that it may contribute significantly (≈90%) to the measured symmetric voltage. This study is expected to be very useful for fully understanding the spin pumping induced dc voltages in metallic FMs with disordered interfaces and large anomalous Hall effect.
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Liu, Qianbiao, i Lijun Zhu. "Current-induced perpendicular effective magnetic field in magnetic heterostructures". Applied Physics Reviews 9, nr 4 (grudzień 2022): 041401. http://dx.doi.org/10.1063/5.0116765.
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The generation of perpendicular effective magnetic field or perpendicular spins ( σz) is central for the development of energy-efficient, scalable, and external-magnetic-field-free spintronic memory and computing technologies. Here, we report the first identification and the profound impacts of a significant effective perpendicular magnetic field that can arise from asymmetric current spreading within magnetic microstrips and Hall bars. This effective perpendicular magnetic field can exhibit all the three characteristics that have been widely assumed in the literature to “signify” the presence of a flow of σz, i.e., external-magnetic-field-free current switching of uniform perpendicular magnetization, a sin 2 φ-dependent contribution in spin-torque ferromagnetic resonance signal of in-plane magnetization ( φ is the angle of the external magnetic field with respect to the current), and a φ-independent but field-dependent contribution in the second harmonic Hall voltage of in-plane magnetization. This finding suggests that it is critical to include current spreading effects in the analyses of various spin polarizations and spin–orbit torques in the magnetic heterostructure. Technologically, our results provide a perpendicular effective magnetic field induced by asymmetric current spreading as a novel, universally accessible mechanism for efficient, scalable, and external-magnetic-field-free magnetization switching in memory and computing technologies.
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Lone, Aijaz H., S. Amara i H. Fariborzi. "Magnetic tunnel junction based implementation of spike time dependent plasticity learning for pattern recognition". Neuromorphic Computing and Engineering 2, nr 2 (25.03.2022): 024003. http://dx.doi.org/10.1088/2634-4386/ac57a2.
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Abstract We present a magnetic tunnel junction (MTJ) based implementation of the spike time-dependent (STDP) learning for pattern recognition applications. The proposed hybrid scheme utilizes the spin–orbit torque (SOT) driven neuromorphic device-circuit co-design to demonstrate the Hebbian learning algorithm. The circuit implementation involves the (MTJ) device structure, with the domain wall motion in the free layer, acting as an artificial synapse. The post-spiking neuron behaviour is implemented using a low barrier MTJ. In both synapse and neuron, the switching is driven by the SOTs generated by the spin Hall effect in the heavy metal. A coupled model for the spin transport and switching characteristics in both devices is developed by adopting a modular approach to spintronics. The thermal effects in the synapse and neuron result in a stochastic but tuneable domain wall motion in the synapse and a superparamagnetic behaviour of in neuron MTJ. Using the device model, we study the dimensional parameter dependence of the switching delay and current to optimize the device dimensions. The optimized parameters corresponding to synapse and neuron are considered for the implementation of the Hebbian learning algorithm. Furthermore, cross-point architecture and STDP-based weight modulation scheme is used to demonstrate the pattern recognition capabilities by the proposed neuromorphic circuit.
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Kim, Yun Ki, i J. B. Ketterson. "Anomalous Magneto-Electric Properties in Chalcopyrite MnGeP2 Films". Applied Mechanics and Materials 864 (kwiecień 2017): 111–15. http://dx.doi.org/10.4028/www.scientific.net/amm.864.111.
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We have successfully grown MnGeP2 thin films and Ge and MnGeP2 alloy films on GaAs(100) substrate. Magnetization measurements have been performed on MnGeP2 film samples at temperatures from 5 to 400 K. The measurements have shown that there are a ferromagnetic to paramagnetic transition above room temperature. Field dependent magnetization experiments have shown a coercive field of 160, 1400, 3900 Oe at 300, 250 and 5 K, respectively. A negative magnetoresistance (MR) has been found with a maximum change less than 2% at 5 T and 5 K. The MR measurements on the films have displayed hysteric behaviors with respect to the external field sweep at low fields at temperature below the ferromagnetic transition. Anomalous Hall effects have been found in the MnGeP2 film and Ge and MnGeP2 alloy film samples. Above the transition temperature neither hysteric behavior nor anomalous Hall effect was found. These results imply that spin polarized hole carriers exist in the MnGeP2 films.
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Vegesna, Sahitya V., Sai V. Lanka, Danilo Bürger, Zichao Li, Sven Linzen i Heidemarie Schmidt. "Analysis of Low-Temperature Magnetotransport Properties of NbN Thin Films Grown by Atomic Layer Deposition". Magnetochemistry 8, nr 3 (9.03.2022): 33. http://dx.doi.org/10.3390/magnetochemistry8030033.
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Superconducting niobium nitride (NbN) films with nominal thicknesses of 4 nm, 5 nm, 7 nm, and 9 nm were grown on sapphire substrates using atomic layer deposition (ALD). We observed probed Hall resistance (HR) (Rxy) in external out-of-plane magnetic fields up to 6 T and magnetoresistance (MR) (Rxx) in external in-plane and out-of-plane magnetic fields up to 6 T on NbN thin films in Van der Pauw geometry. We also observed that positive MR dominated. Our study focused on the analysis of interaction and localisation effects on electronic disorder in NbN in the normal state in temperatures that ranged from 50 K down to the superconducting transition temperature. By modelling the temperature and magnetic field dependence of the MR data, we extracted the temperature-dependent Coulomb interaction constants, spin–orbit scattering lengths, localisation lengths, and valley degeneracy factors. The MR model allowed us to distinguish between interaction effects (positive MR) and localisation effects (negative MR) for in-plane and out-of-plane magnetic fields. We showed that anisotropic dephasing scattering due to lattice non-idealities in NbN could be neglected in the ALD-grown NbN thin films.
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Tiwari, Dhananjay. "Improving signal-to-noise ratio of magnetic tunnel junction based radio frequency detector via spin-torque ferromagnetic resonance". Review of Scientific Instruments 93, nr 5 (1.05.2022): 053904. http://dx.doi.org/10.1063/5.0087860.
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This article focuses on the spin-torque ferromagnetic resonance (STFMR) technique, which was developed and optimized to investigate spin-transfer effects in magnetic tunnel junctions (MTJ) and spin Hall effect phenomena in ferromagnet/non-magnetic heavy metal bilayer systems. The devices for STFMR are typically fabricated with co-planar waveguides with contact pads for applying radio frequency or direct current, Irf(Idc). The device under investigation was a CoFeB/MgO/CoFeB based MTJ with a resistance-area product of 1.5 Ω ( μm)2 having a circular cross section with a diameter of 180 nm and tunneling magneto-resistance in the range of 60%–80%. The development of the STFMR setup and its optimization for achieving higher signal-to-noise ratio (SNR) is discussed using two modulation schemes, namely, radio-frequency modulation and field modulation (FM). The FM-STFMR method reduces frequency-dependent noise and offers a higher SNR of 30 dB compared to other modulation schemes in the literature. In addition, a vector network analyzer based STFMR technique is developed, which provides a simple and fast means for characterizing MTJ devices. Furthermore, to calculate the exact power reaching the MTJ, impedance mismatch is calculated using the de-embedding method. The magnitude of in-plane torkance and out-of-plane torkance with dc bias is measured, and the results are found to be consistent with the results of STFMR techniques. The results show that the magnitude of out-of-plane torkance is substantially smaller than that of in-plane torkance in MTJ.
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Al-Azawi, A. Mohammed, Hayder J. Al-Asedy, Noriah Bidin i Khaldoon N. Abbs. "ZnO QDs Deposited on Si by Sol-Gel Method: Role of Annealing Temperature on Structural and Optical Properties". Modern Applied Science 10, nr 4 (13.01.2016): 12. http://dx.doi.org/10.5539/mas.v10n4p12.
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Zinc acetate, propanol, and ethanolamine are used to synthesize ZnO quantum dots (QDs) via the sol–gel method. Spin coating at 220°C is then employed to prepare ZnO thin films consist of QDs. The effects of thermal annealing temperature on the structural and optical properties of the samples are investigated. The prepared QDs are characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and photoluminescence spectroscopy (PL). XRD patterns reveal the crystalline nature of samples existing in the hexagonal wurtzite phase. Increasing annealing temperatures bring about changes to the crystal orientation through the c-axis and increase the size of the QDs from ~10 nm to ~22 nm; this increment can be explained by a coarsening mechanism and the Ostwald ripening process. The observed broadening of X-ray peaks confirms the evolution of crystalline phases in the ZnO QDs. Quantitative analysis of size-dependent strain effects is performed through the Williamson-Hall model. The QD mean size estimated from FESEM and XRD displays high consistency. Room-temperature PL peaks of 3.37ev are attributed to the radiative recombination of electrons and holes from the ZnO QDs/Si interface.
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Wang, Ziqiang. "Strongly Correlated Fermi Liquid and the Normal State of High Tc Superconductors". International Journal of Modern Physics B 06, nr 05n06 (marzec 1992): 603–54. http://dx.doi.org/10.1142/s0217979292000384.
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New insights into the strongly correlated Fermi liquid state of the SU(N) infinite-U Hubbard and t-J models are presented in connection to the metallic state of unbroken symmetry of the copper oxide planes. The nature of single particle and collective excitations is analyzed and the Landau Fermi Liquid parameters are derived. The one-particle spectral function in the Hubbard valence band is obtained with both Hubbard and Gutzwiller-like features. A simple interpretation of the large incoherent background is given in terms of a superposition of quasiparticles and a collective mode describing the propagation of a bare hole in a large U system. The spin exchange interactions produce very low lying collective modes describing the propagation of staggered spin chirality which soften at incommensurate wavevectors. The quasiparticles are strongly scattered by the low lying chirality fluctuations resulting in deviations from canonical Fermi liquid behavior at low energy scales. Of the same origin, the quasiparticle self energy is found to be strongly k-dependent. It leads to corrections to the dispersion and enhancement of the quasiparticle lifetime in the hole-like region of the interacting Fermi surface. The combined effects are sufficient to produce a sign change in the Hall coefficient evaluated for parameters relevant to the copper oxide planes. We show that these models also exhibit a zero temperature fluctuation driven transition from Fermi liquid to non Fermi liquid phase without the onset of magnetic ordering below a critical doping δc=1/4N, whereby providing a microscopic mechanism for the destruction of the Fermi liquid coherence by strong longitudinal gauge fluctuations which represent the effects of the infinite-U constraint.
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Bakhmetiev, M., O. Koplak, J. L. Bello, S. Mangin i R. Morgunov. "Evolution of switching fields caused by reorientation of GdFeCo/Ir/GdFeCo synthetic ferrimagnet in magnetic field". Journal of Applied Physics 133, nr 10 (14.03.2023): 103903. http://dx.doi.org/10.1063/5.0137287.
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Anomalous Hall effect (AHE) in GdFeCo/Ir/GdFeCo multilayered structures attracts great interest because all optical switching, spin-torque, and other effects promise effective application for ultrafast memory element creation. Since AHE is controlled by GdFeCo magnetization, domain dynamics has importance for practical applications. In our work, magnetization reversal in perpendicular GdFeCo/Ir/GdFeCo synthetic ferrimagnets is characterized by AHE measurements. The AHE hysteresis loop obtained with the field applied perpendicular to the sample plane is composed of three sub-loops, and two of them are symmetrically biased with respect to the third one. Switching magnetic fields for two of the three transitions are found to be dependent on magnetic history. In particular, exposure of the sample in the in-plane field leads to reduction of the out-of-plane switching fields in side sub-loops. A multiple series of perpendicular hysteresis loops recorded after exposure under high in-plane field reveals gradual (within 30 min) relaxation of the out-of-plane switching fields to their initial values observed in a non-magnetized sample. Domain wall mobility, limiting switching of the bilayer devices, is complicated due to the coupling between partial domains in each single layer. Unusual dynamics of double domain walls results in unexpected new phenomena affecting electrical processes in bilayer structures.
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Thouless, David. "ANDERSON LOCALIZATION IN THE SEVENTIES AND BEYOND". International Journal of Modern Physics B 24, nr 12n13 (20.05.2010): 1507–25. http://dx.doi.org/10.1142/s0217979210064496.
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Little attention was paid to Anderson's challenging paper on localization for the first ten years, but from 1968 onwards it generated a lot of interest. Around that time a number of important questions were raised by the community, on matters such as the existence of a sharp distinction between localized and extended states, or between conductors and insulators. For some of these questions the answers are unambiguous. There certainly are energy ranges in which states are exponentially localized, in the presence of a static disordered potential. In a weakly disordered one-dimensional potential, all states are localized. There is clear evidence, in three dimensions, for energy ranges in which states are extended, and ranges in which they are diffusive. Magnetic and spin-dependent interactions play an important part in reducing localization effects. For massive particles like electrons and atoms the lowest energy states are localized, but for massless particles like photons and acoustic phonons the lowest energy states are extended. Uncertainties remain. Scaling theory suggests that in two-dimensional systems all states are weakly localized, and that there is no minimum metallic conductivity. The interplay between disorder and mutual interactions is still an area of uncertainty, which is very important for electronic systems. Optical and dilute atomic systems provide experimental tests which allow interaction to be much less important. The quantum Hall effect provided a system where states on the Fermi surface are localized, but non-dissipative currents flow in response to an electric field.
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Qin, Dan, Zhengting Jiang, Peng Yan, Qihong Wu i Guangqian Ding. "Superior spin transport properties based on VS2 and VCl2 ferromagnetic monolayers". Journal of Applied Physics 132, nr 21 (7.12.2022): 213902. http://dx.doi.org/10.1063/5.0124820.
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Two-dimensional ferromagnetic monolayers have attracted growing interest due to their promising applications in spintronic devices. To explore the potential application of monolayer VS2 and VCl2 in spintronic devices, previously reported ferromagnetic semiconductor and half-metal, respectively, we investigate the spin transport properties of VS2 homo-junction, VCl2 homo-junction, and lateral VS2–VCl2 heterostructure using first-principles combined with non-equilibrium Green's function. We show that monolayer VS2 exhibit superior spin Seebeck effect along an armchair direction, monolayer VCl2 is an excellent platform to realize a spin valve, and the magnetoresistance ratio is up to 1.3 × 104. Moreover, the VS2–VCl2 heterostructure exhibits an excellent spin diode effect. We explain these effects from the calculated spin-dependent band structure and transmission spectrum. The superior spin transport properties make monolayer VS2 and VCl2 promising candidates for spintronic applications.
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Bai, Jing, Jiaying Ji, Liyu Hao, Tie Yang i Xingwen Tan. "DFT Investigation on the Electronic, Magnetic, Mechanical Properties and Strain Effects of the Quaternary Compound Cu2FeSnS4". Crystals 10, nr 6 (15.06.2020): 509. http://dx.doi.org/10.3390/cryst10060509.
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The electronic, magnetic and mechanical properties of the quaternary compound Cu2FeSnS4 have been investigated with first principle calculations. Its half-metallicity has been identified with spin polarized band structures and its magnetic origination is caused by the strong spin splitting effect in the d orbitals of Fe atoms. The total magnetic moment of 4 μB is mainly contributed by the Fe atoms and the spatial distribution of the magnetic spin density and charge density difference have also been examined. Moreover, several mechanical properties of Cu2FeSnS4 have been derived and its mechanical stability is also verified. The directional dependent Young’s modulus exhibits relatively small anisotropy yet the shear modulus shows strong directional anisotropy. At last, the tetragonal strain effects have been evaluated and their impact on the electronic and magnetic properties are provided. Results show the total magnetic moment stays almost unchanged while the half-metallicity can only be maintained under relatively small variations for both strains. This study can provide comprehensive information about the various properties of Cu2FeSnS4 compound and serve as a helpful reference for its future applications.
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PFEIFFER, Silvia, C. F. Antonius GORREN, Eva PITTERS, Kurt SCHMIDT, R. Ernst WERNER i Bernd MAYER. "Allosteric modulation of rat brain nitric oxide synthase by the pterin-site enzyme inhibitor 4-aminotetrahydrobiopterin". Biochemical Journal 328, nr 2 (1.12.1997): 349–52. http://dx.doi.org/10.1042/bj3280349.
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We investigated the functional and allosteric effects of the 4-amino analogue of tetrahydrobiopterin, (6R)-2,4-diamino-5,6,7,8-tetrahydro-6-(l-erythro-1,2-dihydroxypropyl)pteridine (4-amino-H4biopterin) on pteridine-free rat neuronal nitric oxide synthase. In the presence of added (6R)-5,6,7,8-tetrahydro-L-erythrobiopterin (H4biopterin; 10 μM), 4-amino-H4biopterin completely inhibited the conversion of both L-arginine and NG-hydroxy-L-arginine with half-maximally effective concentrations of 1.1±0.09 and 1.3±0.09 μM, respectively. Inhibition was reversible, as shown by a time-dependent restoration of citrulline formation upon dilution of the inhibitor-treated enzyme (t1/2 = 3.0 min). Binding of 4-amino-H4biopterin led to a complete conversion of the haem from low-spin to high-spin state, and to the formation of stable homodimers which partially survived electrophoresis under denaturating conditions. These results show that oxidation of both L-arginine and NG-hydroxy-L-arginine is pteridine-dependent, and that the allosteric effects of H4biopterin do not fully explain the essential role of the pteridine cofactor in nitric oxide biosynthesis.
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Demchenko, D. O., A. N. Chantis i A. G. Petukhov. "SPIN FILTERING IN MAGNETIC HETEROSTRUCTURES". International Journal of Modern Physics B 15, nr 24n25 (10.10.2001): 3247–52. http://dx.doi.org/10.1142/s0217979201007579.
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Several techniques were proposed to achieve solid state spin filtering such as magnetic tunnel junctions comprised of half-metallic compounds or solid state Stern-Gerlach apparatus. Another alternative consists in using spin-dependent resonant tunneling through magnetically active quantum wells. Recent advances in molecular beam epitaxial growth made it possible to fabricate exotic heterostructures comprised of magnetic films or buried layers (ErAs, GaxMn1-xAs) integrated with conventional semiconductors (GaAs) and to explore quantum transport in these heterostructures. It is particularly interesting to study spin-dependent resonant tunneling in double-barrier resonant tunneling diodes (RTD) with magnetic elements such as GaAs/AlAs/ErAs/AlAs/ErAs/AlAs/GaAs, GaxMn1-xAs/AlAs/GaAs/AlAs/GaAs, and GaAs/AlAs/GaxMn1-xAs/AlAs/GaAs. We present the results of our theoretical studies and computer simulations of transmission coefficients and current-voltage characteristics of resonant tunneling diodes based on these double-barrier structures. Resonant tunneling of holes (GaxMn1-xAs-based RTDs) is considered. Our approach is based on k·p perturbation theory with exchange splitting effects taken into account. We analyze exchange splitting of different resonant channels as a function of magnetization as well as spin polarization of the transmitted current as a function of bias. We found that resonant tunneling I – V characteristics of the double-barrier magnetic hererostructures strongly depend on the doping level in the emitter as well as on the orientation of the magnetization.
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Annveer, Rahul Gauram, Rishi P. Singh, Arvind Kumar VERMA i Praveen Kumar. "Study of Magnetic, Optical, Electronic and Thermodynamic Effects in Thallium Rare Earth Disulphides (TlRES2, RE= Tb- Er)". Materials Plus 2, nr 1 (16.06.2023): 20–34. http://dx.doi.org/10.37256/mp.2120232857.
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In the present research work, we have investigated density of electronic states, electronic band structure, magnetic structure, optical spectra and temperature dependent thermodynamic characteristics of thallium rare earth sulphides, TlRES2 (RE: Tb-Er) using FP-LAPW method and PBE-GGA exchange correlation within DFT. The electronic structure pointed out that TlRES2 compounds show half metallic character. The magnetic moment and spin polarization calculations prove that TlRES2 are fully spin polarized compounds with ferromagnetic nature. Optical spectra show that intraband transitions occur in infrared (IR) regime due to half metallic character of TlRES2 and behave as opaque in ultraviolet (UV) region. High refractive index in IR regime also show metallic character and high peak in UV regime show slow propagation of light in UV regime. The reflection coefficient is found maximum (~50–60%) in UV regime. Greater energy loss has been seen on the higher energy side, which corresponds to the stimulation of plasmons by electrons moving through the compounds. Plasma resonances lead to the frequent peaks at ~ 6.0 eV, 11.0 eV, and 12.0 eV. According to calculations made using the quasi-harmonic Debye model, TlRES2 compounds are dimensionally less stable (i.e., much hard), have poor thermal conductivity, and experience faster-than-average disorder with increasing the temperature.
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Ohler, Simon, Maximilian Kiefer-Emmanouilidis, Antoine Browaeys, Hans Peter Büchler i Michael Fleischhauer. "Self-generated quantum gauge fields in arrays of Rydberg atoms". New Journal of Physics 24, nr 2 (1.02.2022): 023017. http://dx.doi.org/10.1088/1367-2630/ac4a15.
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Abstract As shown in recent experiments (Lienhard et al 2020 Phys. Rev. X 10 021031), spin–orbit coupling in systems of Rydberg atoms can give rise to density-dependent Peierls phases in second-order hoppings of Rydberg spin excitations and nearest-neighbor repulsion. We here study theoretically a one-dimensional zig-zag ladder system of such spin–orbit coupled Rydberg atoms at half filling. The second-order hopping is shown to be associated with an effective gauge field, which in mean-field approximation is static and homogeneous. Beyond the mean-field level the gauge potential attains a transverse quantum component whose amplitude is dynamical and linked to density modulations. We here study the effects of this to the possible ground-state phases of the system. In a phase where strong repulsion leads to a density wave, we find that as a consequence of the induced quantum gauge field a regular pattern of current vortices is formed. However also in the absence of density–density interactions the quantum gauge field attains a non-vanishing amplitude. Above a certain critical strength of the second-order hopping the energy gain due to gauge-field induced transport overcomes the energy cost from the associated build-up of density modulations leading to a spontaneous generation of the quantum gauge field.
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Dolui, Sudipto, Ze Wang, Danny JJ Wang, Raghav Mattay, Mack Finkel, Mark Elliott, Lisa Desiderio i in. "Comparison of non-invasive MRI measurements of cerebral blood flow in a large multisite cohort". Journal of Cerebral Blood Flow & Metabolism 36, nr 7 (3.05.2016): 1244–56. http://dx.doi.org/10.1177/0271678x16646124.
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Arterial spin labeling and phase contrast magnetic resonance imaging provide independent non-invasive methods for measuring cerebral blood flow. We compared global cerebral blood flow measurements obtained using pseudo-continuous arterial spin labeling and phase contrast in 436 middle-aged subjects acquired at two sites in the NHLBI CARDIA multisite study. Cerebral blood flow measured by phase contrast (CBFPC: 55.76 ± 12.05 ml/100 g/min) was systematically higher ( p < 0.001) and more variable than cerebral blood flow measured by pseudo-continuous arterial spin labeling (CBFPCASL: 47.70 ± 9.75). The correlation between global cerebral blood flow values obtained from the two modalities was 0.59 ( p < 0.001), explaining less than half of the observed variance in cerebral blood flow estimates. Well-established correlations of global cerebral blood flow with age and sex were similarly observed in both CBFPCASL and CBFPC. CBFPC also demonstrated statistically significant site differences, whereas no such differences were observed in CBFPCASL. No consistent velocity-dependent effects on pseudo-continuous arterial spin labeling were observed, suggesting that pseudo-continuous labeling efficiency does not vary substantially across typical adult carotid and vertebral velocities, as has previously been suggested. Conclusions: Although CBFPCASL and CBFPC values show substantial similarity across the entire cohort, these data do not support calibration of CBFPCASL using CBFPC in individual subjects. The wide-ranging cerebral blood flow values obtained by both methods suggest that cerebral blood flow values are highly variable in the general population.
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Lawaczeck, R., H. Bauer, T. Frenzel, M. Hasegawa, Y. Ito, K. Kito, N. Miwa, H. Tsutsui, H. Vogler i H. J. Weinmann. "Magnetic Iron Oxide Particles Coated with Carboxydextran for Parenteral Administration and Liver Contrasting". Acta Radiologica 38, nr 4 (lipiec 1997): 584–97. http://dx.doi.org/10.1080/02841859709174391.
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Rationale and objectives: To evaluate the physical and pharmacological profiles of SH U555A, a suspension of magnetic iron oxide particles that is designed to enhance the visualization of liver tumors and metastases. Material and Methods: Chemical and physical methods were used to characterize the size and structure of these magnetic iron oxide particles in aqueous solution. The biodistribution and pharmacokinetics of the particles were studied in mice, rats and dogs. The imaging efficacy of the particles was demonstrated by MR imaging in rat liver tumors Results: The SH U555A particles consist of low-molecular-weight carboxydextran-coated iron oxides predominantly of the γ-Fe2O3 form with a hydrodynamic diameter ranging from 57-59 nm and strong T2 relaxivity of 164 liters * mmol−1 * S−1 (water, 0.47 T). In rats the particles exhibited a dose-dependent half-life of between 2 and 3 days in the liver at a dose of 20 μmol Fe/kg and a shorter half-life at lower doses. No major side effects were found. In a rat tumor model the tumor-to-liver contrast was markedly improved after i.v. administration of SH U555A. At a dose of 14 μmol Fe/kg the half-maximal contrast-effect was obtained even in nonoptimized T1-weighted spin-echo images. Conclusion: SH U555A is a superparamagnetic MR contrast agent for i.v. administration and has substantial potential for the demarcation of liver tumors.
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Zhdanov, V., E. Fedorova i M. Khelashvili. "Form of a microlensed line from accretion disk in the linear caustic approximation". Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, nr 57 (2018): 27–31. http://dx.doi.org/10.17721/btsnua.2018.57.27-31.
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The line profiles like that of the fluorescent Fe K or Co K lines in the X-ray spectra of the active galactic nuclei (AGN) reflect characteristics of the central regions of these objects. These lines can be formed in the accretion disks around central supermassive black holes and their shapes are connected with the central black hole spin and the accretion disk inclination angle to the line-of-the-sight. If an AGN is a source of a gravitational lens system with microlensing events, one can get an additional important information about both the accretion disk parameters and gravitational lens parameters as well. Microlensing processes were observed in such gravitational lens systems, as PKS 1830-211, B0218+357, RX J1131-1231 i HE1104-1805, Q2237+0305 and we can suspect to observe there also the spectral appearances of microlensing. Here we performed the numerical simulations of the microlensed relativistic spectral line profiles formed in the AGN accretion disks. Using the inear caustic model we show that the time dependence of the profile is determined essentially by the angle between to the disk axis and the caustic. This gives us an opportunity to assess this orientation. Microlens caustics magnify some parts of the accretion disk more prominently than others. Due to the Doppler effects and differences in the rotation direction this leads to the frequency-dependent magnification which distorts the profile of a relativistic spectral line. Such deformations are variable with time due to relative motions of the source and the microlens, and they can give us possibility to obtain some additional information about the disk brightness profile and caustic orientation relatively to the disk. Here we consider the thin disk model, Schwarzschild black hole, and the linear caustic approximation as well. The numerical simulations of the relativistic emission line profiles distorted by strong gravitational microlensing effect were performed for several different orientations of the linear caustic relatively to the disk, as well as several inclinations of the disk to the line-of-the-sight. Basic presumptions for the numerical modeling were the following: (a) AGN is a source in the gravitational lens system and it its inner parts the luminescent emission lines with relativistic profiles are being emitted; (b) this line is formed in the thin accretion disk quite far away from the central black hole and can be calculated with no taking into account the relativistic effects; (c) the caustic can be considered as a linear one. We show that the relative orientation of the caustic and the disk can be determined from emission lines profiles. Our numerical simulations demonstrate that the difference between profiles corresponding to different caustic orientations appears to be more prominent during the first half of the strong microlensing event, namely, before the crossing the disk center, and this dependence is irrespective to the accretion disk brightness profile. We show that for the spectral accuracy level high enough we have a perspective to determine the caustic orientation from the observational data.
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Andersson, Lars, i Marius Adrian Oancea. "Spin Hall effects in the sky". Classical and Quantum Gravity, 20.06.2023. http://dx.doi.org/10.1088/1361-6382/ace021.
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Abstract In many areas of physics, the propagation of wave packets carrying intrinsic angular momentum is generally influenced by spin-orbit interactions. This is the main mechanism behind spin Hall effects, which result in wave packets following spin-dependent trajectories. Spin Hall effects have been observed in several experiments for electrons in condensed matter systems and for light propagating in inhomogeneous optical media. Similar effects have also been predicted for wave packets propagating in inhomogeneous gravitational fields. We give a brief introduction to gravitational spin Hall effects, emphasizing the analogies with the spin Hall effect of light in optics. Furthermore, we review the most promising astrophysical avenues that could lead to experimental observations of the gravitational spin Hall effect.
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Cramer, Joel, Andrew Ross, Samridh Jaiswal, Lorenzo Baldrati, Romain Lebrun i Mathias Kläui. "Orientation-dependent direct and inverse spin Hall effects in Co60Fe20B20". Physical Review B 99, nr 10 (11.03.2019). http://dx.doi.org/10.1103/physrevb.99.104414.
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Yahagi, Yuta, Daisuke Miura i Akimasa Sakuma. "Perpendicularly Polarized Spin Hall Effects Induced by Spin-Dependent Scattering in Ferromagnetic Metals". Journal of the Physical Society of Japan 91, nr 8 (15.08.2022). http://dx.doi.org/10.7566/jpsj.91.083701.
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Zadorozhnyi, Andrei, i Yuri Dahnovsky. "Temperature effects in spin-dependent Hall currents in an ideal skyrmion gas". Physical Review B 103, nr 18 (18.05.2021). http://dx.doi.org/10.1103/physrevb.103.184418.
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Kang, Sungmo, Seungjin Kang, Heung-Sik Kim i Jaejun Yu. "Field-controlled quantum anomalous Hall effect in electron-doped CrSiTe3 monolayer". npj 2D Materials and Applications 7, nr 1 (4.03.2023). http://dx.doi.org/10.1038/s41699-023-00375-3.
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AbstractWe report Chern insulating phases emerging from a single layer of layered chalcogenide CrSiTe3, a transition metal trichacogenides (TMTC) material, in the presence of charge doping. Due to strong hybridization with Te p orbitals, the spin-orbit coupling effect opens a finite band gap, leading to a nontrivial topology of the Cr eg conduction band manifold with higher Chern numbers. Our calculations show that quantum anomalous Hall effects can be realized by adding one electron in a formula unit cell of Cr2Si2Te6, equivalent to electron doping by 2.36 × 1014 cm−2 carrier density. Furthermore, the doping-induced anomalous Hall conductivity can be controlled by an external magnetic field via spin-orientation-dependent tuning of the spin-orbit coupling. In addition, we find distinct quantum anomalous Hall phases employing tight-binding model analysis, suggesting that CrSiTe3 can be a fascinating platform to realize Chern insulating systems with higher Chern numbers.
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Martin-Rio, Sergi, Carlos Frontera, Alberto Pomar, Lluis Balcells i Benjamin Martinez. "Suppression of spin rectification effects in spin pumping experiments". Scientific Reports 12, nr 1 (7.01.2022). http://dx.doi.org/10.1038/s41598-021-04319-z.
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AbstractSpin pumping (SP) is a well-established method to generate pure spin currents allowing efficient spin injection into metals and semiconductors avoiding the problem of impedance mismatch. However, to disentangle pure spin currents from parasitic effects due to spin rectification effects (SRE) is a difficult task that is seriously hampering further developments. Here we propose a simple method that allows suppressing SRE contribution to inverse spin Hall effect (ISHE) voltage signal avoiding long and tedious angle-dependent measurements. We show an experimental study in the well-known Py/Pt system by using a coplanar waveguide (CPW). Results obtained demonstrate that the sign and size of the measured transverse voltage signal depends on the width of the sample along the CPW active line. A progressive reduction of this width evidences that SRE contribution to the measured transverse voltage signal becomes negligibly small for sample width below 200 μm. A numerical solution of the Maxwell equations in the CPW-sample setup, by using the Landau-Lifshitz equation with the Gilbert damping term (LLG) as the constitutive equation of the media, and with the proper set of boundary conditions, confirms the obtained experimental results.
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Maruyama, Yuu, Ryo Ohshima, Ei Shigematsu, Yuichiro Ando i Masashi Shiraishi. "Modulation of Hanle magnetoresistance in an ultrathin platinum film by ionic gating". Applied Physics Express, 14.02.2023. http://dx.doi.org/10.35848/1882-0786/acbc0a.
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Abstract Hanle magnetoresistance (HMR) is a type of magnetoresistance where interplay of the spin Hall effect, Hanle-type spin precession, and spin-dependent scattering at the top/bottom surfaces in a heavy metal controls the effect. In this study, we modulate HMR in ultrathin Pt by ionic gating, where the surface Rashba field created by a strong electric field at the interface between the ionic gate and Pt plays the dominant role in the modulation. This finding can facilitate investigations of gate-tunable, spin-related effects and fabrication of spin devices.
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Liang, Chengkang, Dongxue Liu, Rao Liu, Dongmei Deng i Guanghui Wang. "Chirality-modulated photonic spin Hall effect in PT-symmetry". Nanophotonics, 28.06.2022. http://dx.doi.org/10.1515/nanoph-2022-0229.
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Abstract The photonic spin Hall effect (PSHE), featured by a spin-dependent shift driven by its polarization handedness, is proposed to facilitate the applications in precision metrology and quantum information processing. Here, due to the magnetoelectric coupling of the chirality, the PSHE is accompanied with Goos–Hänchen and Imbert–Fedorov effects. Taking advantage of this superiority, the transverse shift (TS) and longitudinal shift (LS) can be applied simultaneously. Rearranging the PT-symmetric scattering matrix, the responsive PSHE near the exceptional points and their basic physical mechanisms are discussed in detail in the case of complex chirality κ. Re[κ] and Im[κ] regulated the rich (at multi-angle), gaint (reach upper limit) and tunable (magnitude and direction) TS and LS, respectively. Based on the chirality-modulated PSHE, the novel applications in binary code conversion and barcode encryption are proposed systematically. By incorporating the quantum weak measurement technology, our applications provide new mechanisms to realize optoelectronic communication.
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Wijewardena, U. Kushan, Tharanga R. Nanayakkara, Annika Kriisa, Christian Reichl, Werner Wegscheider i Ramesh G. Mani. "Size dependence- and induced transformations- of fractional quantum Hall effects under tilted magnetic fields". Scientific Reports 12, nr 1 (10.11.2022). http://dx.doi.org/10.1038/s41598-022-22812-x.
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AbstractTwo-dimensional electron systems subjected to high transverse magnetic fields can exhibit Fractional Quantum Hall Effects (FQHE). In the GaAs/AlGaAs 2D electron system, a double degeneracy of Landau levels due to electron-spin, is removed by a small Zeeman spin splitting, $$g \mu _B B$$ g μ B B , comparable to the correlation energy. Then, a change of the Zeeman splitting relative to the correlation energy can lead to a re-ordering between spin polarized, partially polarized, and unpolarized many body ground states at a constant filling factor. We show here that tuning the spin energy can produce fractionally quantized Hall effect transitions that include both a change in $$\nu$$ ν for the $$R_{xx}$$ R xx minimum, e.g., from $$\nu = 11/7$$ ν = 11 / 7 to $$\nu = 8/5$$ ν = 8 / 5 , and a corresponding change in the $$R_{xy}$$ R xy , e.g., from $$R_{xy}/R_{K} = (11/7)^{-1}$$ R xy / R K = ( 11 / 7 ) - 1 to $$R_{xy}/R_{K} = (8/5)^{-1}$$ R xy / R K = ( 8 / 5 ) - 1 , with increasing tilt angle. Further, we exhibit a striking size dependence in the tilt angle interval for the vanishing of the $$\nu = 4/3$$ ν = 4 / 3 and $$\nu = 7/5$$ ν = 7 / 5 resistance minima, including “avoided crossing” type lineshape characteristics, and observable shifts of $$R_{xy}$$ R xy at the $$R_{xx}$$ R xx minima- the latter occurring for $$\nu = 4/3, 7/5$$ ν = 4 / 3 , 7 / 5 and the 10/7. The results demonstrate both size dependence and the possibility, not just of competition between different spin polarized states at the same $$\nu$$ ν and $$R_{xy}$$ R xy , but also the tilt- or Zeeman-energy-dependent- crossover between distinct FQHE associated with different Hall resistances.
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Da, H. X., Qi Song, Pengya Hu i Huapeng Ye. "Enhanced Photonic Spin Hall effect in Dirac Semimetal Metamaterial Enabled by Zero Effective Permittivity". Nanotechnology, 2.12.2022. http://dx.doi.org/10.1088/1361-6528/aca80e.
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Abstract With the recent discovery of three dimensional Dirac semimetals, their integrations with the optoelectronic devices allow the novel optical effects and functionalities. Here, we theoretically report the photonic spin Hall effect in a periodic structure, where three dimensional Dirac semimetals and the dielectric materials are assembled into the stack. The incident angle and frequency dependent spin shift spectrum reveals that the spin shifts of the transmitted wave in this structure emerge the obvious peaks and valleys for the horizontal polarized wave and their magnitudes and positions display a distinct dependence on the incident angle around the specific frequency. These observations originate from its zero value of the effective perpendicular permittivity and its greatly reduced transmission in the multilayered structure, whose mechanism is different from those in the previous works. Moreover, both the peaks and valleys of the transmitted spin shift are significantly sensitive to the Fermi energy of three dimensional Dirac semimetals, whose magnitudes and positions can be tuned by varying it. Our results highlight the vital role of three dimensional Dirac semimetals in their applications of the spin photonic devices and pave the way to explore the tunable photonic spin Hall effect by engineering their Fermi energies.
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Wang, Shubo, Guanqing Zhang, Xulong Wang, Qing Tong, Jensen Li i Guancong Ma. "Spin-orbit interactions of transverse sound". Nature Communications 12, nr 1 (21.10.2021). http://dx.doi.org/10.1038/s41467-021-26375-9.
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AbstractSpin-orbit interactions (SOIs) endow light with intriguing properties and applications such as photonic spin-Hall effects and spin-dependent vortex generations. However, it is counterintuitive that SOIs can exist for sound, which is a longitudinal wave that carries no intrinsic spin. Here, we theoretically and experimentally demonstrate that airborne sound can possess artificial transversality in an acoustic micropolar metamaterial and thus carry both spin and orbital angular momentum. This enables the realization of acoustic SOIs with rich phenomena beyond those in conventional acoustic systems. We demonstrate that acoustic activity of the metamaterial can induce coupling between the spin and linear crystal momentum k, which leads to negative refraction of the transverse sound. In addition, we show that the scattering of the transverse sound by a dipole particle can generate spin-dependent acoustic vortices via the geometric phase effect. The acoustic SOIs can provide new perspectives and functionalities for sound manipulations beyond the conventional scalar degree of freedom and may open an avenue to the development of spin-orbit acoustics.
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Ma, Teng, Hao Chen, Kunihiro Yananose, Xin Zhou, Lin Wang, Runlai Li, Ziyu Zhu i in. "Growth of bilayer MoTe2 single crystals with strong non-linear Hall effect". Nature Communications 13, nr 1 (17.09.2022). http://dx.doi.org/10.1038/s41467-022-33201-3.
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Abstract The reduced symmetry in strong spin-orbit coupling materials such as transition metal ditellurides (TMDTs) gives rise to non-trivial topology, unique spin texture, and large charge-to-spin conversion efficiencies. Bilayer TMDTs are non-centrosymmetric and have unique topological properties compared to monolayer or trilayer, but a controllable way to prepare bilayer MoTe2 crystal has not been achieved to date. Herein, we achieve the layer-by-layer growth of large-area bilayer and trilayer 1T′ MoTe2 single crystals and centimetre-scale films by a two-stage chemical vapor deposition process. The as-grown bilayer MoTe2 shows out-of-plane ferroelectric polarization, whereas the monolayer and trilayer crystals are non-polar. In addition, we observed large in-plane nonlinear Hall (NLH) effect for the bilayer and trilayer Td phase MoTe2 under time reversal-symmetric conditions, while these vanish for thicker layers. For a fixed input current, bilayer Td MoTe2 produces the largest second harmonic output voltage among the thicker crystals tested. Our work therefore highlights the importance of thickness-dependent Berry curvature effects in TMDTs that are underscored by the ability to grow thickness-precise layers.
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Peña Corredor, Antonio, Alberto Anadón, Laurent Schlur, Jérôme Robert, Héloïse Damas, Juan-Carlos Rojas-Sánchez, Sébastien Petit-Watelot, Nathalie Viart, Daniele Preziosi i Christophe Lefevre. "Spin transport properties of spinel vanadate-based heterostructures". Applied Physics Letters 123, nr 7 (14.08.2023). http://dx.doi.org/10.1063/5.0165642.
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Spin–orbit coupling and breaking of inversion symmetry are necessary ingredients to enable a pure spin current-based manipulation of the magnetization via the spin–orbit torque effect. Currently, magnetic insulator oxides with non-dissipative characteristics are being explored. When combined with non-magnetic heavy metals, known for their large spin–orbit coupling, they offer promising potential for energy-efficient spin-orbitronics applications. The intrinsic electronic correlations characterizing those strongly correlated oxides hold the promises to add extra control-knobs to the desired efficient spin-wave propagation and abrupt magnetization switching phenomena. Spinel vanadate FeV2O4 (FVO) exhibits several structural phase transitions, which are accompanied by an intricate interplay of magnetic, charge, and orbital orderings. When grown as a thin film onto SrTiO3, the compressive strain state induces a perpendicular magnetic anisotropy, making FVO-based heterostructures desirable for spin-orbitronics applications. In this study, we have optimized the deposition of stoichiometric and epitaxial Pt/FVO heterostructures by pulsed laser deposition and examined their spin-related phenomena. From angle-dependent magnetotransport measurements, we observed both anisotropic magnetoresistance and spin Hall magnetoresistance (SMR) effects. Our findings show the SMR component as the primary contributor to the overall magnetoresistance, whose high value of 0.12% is only comparable to properly optimized oxide-based systems.
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Keller, S., J. Greser, M. R. Schweizer, A. Conca, V. Lauer, C. Dubs, B. Hillebrands i E. Th Papaioannou. "Relative weight of the inverse spin-Hall and spin-rectification effects for metallic polycrystalline Py/Pt, epitaxial Fe/Pt, and insulating YIG/Pt bilayers: Angular dependent spin pumping measurements". Physical Review B 96, nr 2 (24.07.2017). http://dx.doi.org/10.1103/physrevb.96.024437.
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Farrar, Liam S., Zachary Zajicek, Archie B. Morfoot, Matthew Bristow, Oliver S. Humphries, Amir A. Haghighirad, Alix McCollam, Simon J. Bending i Amalia I. Coldea. "Unconventional localization of electrons inside of a nematic electronic phase". Proceedings of the National Academy of Sciences 119, nr 43 (18.10.2022). http://dx.doi.org/10.1073/pnas.2200405119.
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The magnetotransport behavior inside the nematic phase of bulk FeSe reveals unusual multiband effects that cannot be reconciled with a simple two-band approximation proposed by surface-sensitive spectroscopic probes. In order to understand the role played by the multiband electronic structure and the degree of two-dimensionality, we have investigated the electronic properties of exfoliated flakes of FeSe by reducing their thickness. Based on magnetotransport and Hall resistivity measurements, we assess the mobility spectrum that suggests an unusual asymmetry between the mobilities of the electrons and holes, with the electron carriers becoming localized inside the nematic phase. Quantum oscillations in magnetic fields up to 38 T indicate the presence of a hole-like quasiparticle with a lighter effective mass and a quantum scattering time three times shorter, as compared with bulk FeSe. The observed localization of negative charge carriers by reducing dimensionality can be driven by orbitally dependent correlation effects, enhanced interband spin fluctuations, or a Lifshitz-like transition, which affect mainly the electron bands. The electronic localization leads to a fragile two-dimensional superconductivity in thin flakes of FeSe, in contrast to the two-dimensional high- T c induced with electron doping via dosing or using a suitable interface.
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Jang, Chan Wook, Yusuff Adeyemi Salawu, Jin Hee Kim, Van Quang Nguyen, Min Seop Kim, Sang‐Eon Lee, Hyebin Son i in. "2D Weyl‐Semimetal States Achieved by a Thickness‐Dependent Crossover and Topological Phase Transition in Bi0.96Sb0.04 Thin Films". Advanced Functional Materials, 30.08.2023. http://dx.doi.org/10.1002/adfm.202305179.
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AbstractDespite theoretical expectations for 2D Weyl semimetals (WSMs), realizing stable 2D topological semimetal states experimentally is currently a great challenge. Here, 2D WSM states achieved by a thickness‐dependent topological phase transition from 3D Dirac semimetal to 2D WSM in molecular‐beam‐epitaxy‐grown Bi0.96Sb0.04 thin films are reported. 2D weak anti‐localization (WAL) and chiral anomaly arise in the Bi0.96Sb0.04 films for thicknesses below ≈10 nm, supporting 2D Weyl semimetallic transport in the films. This is particularly evident from magnetoresistance (MR) measurements which show cusp structures at around B = 0, indicating WAL, and negative MR, typical of chiral anomaly, only for layers with thicknesses below ≈10 nm. The temperature dependencies of the dephasing length for various thicknesses are consistent with those of the MR. Analysis based on second harmonic generation, terahertz emission, Seebeck/Hall effects, Raman scattering, X‐ray diffraction, and X‐ray photoemission demonstrates that the Dirac‐ to Weyl‐semimetal phase transition for films thinner than ≈10 nm is induced by inversion‐symmetry breaking due to the lattice‐mismatch strain between the Bi0.96Sb0.04 film and substrate. The realization of 2D WSMs is particularly significant for applications in high‐speed electronics, spintronics, and quantum computations due to their high mobility, chiral spin, and topologically‐protected quantum qubits.
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Thillosen, Nicolas Henri, Thomas Schäpers, Nicoleta Kaluza, Hilde Hardtdegen i Vitaliy Guzenko. "Weak Antilocalization in Polarization-Doped AlGaN/GaN Heterostructures". MRS Proceedings 892 (2005). http://dx.doi.org/10.1557/proc-0892-ff17-02.
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AbstractThe properties of AlGaN/GaN heterostructures have been a subject of great activity because of their application in high frequency, high power, and high temperature devices. Magnetotransport measurements give the possibility to study the properties of a two-dimensional electron gas. Indeed, Shubnikov-de Haas oscillations of a two-dimensional electron gas can be observed at high magnetic fields. Moreover, magnetoresistance measurements close to zero magnetic field give the possibility to investigate the weak localization and weak antilocalization arising from AlGaN/GaN heterostructures. The latter is related to the spin-orbit interaction on the spin of the carriers present in these heterostructures and is a key-feature of the spin-transistor proposed by Datta and Das [1]. As a matter of fact, the spin orientation between the electrodes of this novel device should be manipulated by the controllable strength of the spin-orbit interaction in the two-dimensional electron gas. In order to obtain information on spin-orbit effects in AlGaN/GaN heterostructures we therefore analyzed the weak antilocalization observed in the magnetoresistance.Polarization-doped AlGaN/GaN heterostructures were grown by metalorganic vapor phase epitaxy (MOVPE) on the (0001) surface of sapphire substrates. First a 3 mm-thick GaN buffer layer was grown, followed by a Al0.3Ga0.7N layer with a thickness of 20 nm. Magnetotransport measurements were performed over a magnetic field range from –50 mT to +50 mT at various temperatures between 0.1 and 18 K. The Hall-bars were prepared by optical lithography and Ar+-ion-beam-etching technique. The metals used for the ohmic contacts were Ti/Al/Ni/Au. The mobility and carrier concentration in the single occupied subband were obtained from the Shubnikov-de Haas oscillations with the respective values of 9100 cm2/Vs and 6.2×1012 cm-2.In our case, the Shubnikov-de Haas oscillations of the two-dimensional electron gas reveal the occupation of a single subband in the nearly triangular quantum well. At low magnetic field, weak localization as well as weak antilocalization were observed, showing that strong spin-orbit interaction is present in our structures. A previous report [2] explained the weak-antilocalization as being related to the intersubband scattering due to the occupation of a second subband in a modulation-doped quantum well. We show that weak antilocalization is also present in a polarization-doped quantum well with a single subband being occupied. In this perspective, temperature-dependent weak antilocalization measurements will be presented and analyzed using adequate theoretical models. Finally, the relevant scattering times like elastic scattering time, dephasing time as well as spin-orbit scattering time have been extracted. [1] S. Datta and B. Das, Appl. Phys. Lett. Vol. 56, pp. 665-667, 1990. [2] J. Lu et al., Appl. Phys. Lett., Vol. 85, pp. 3125-3127, 2004
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Wang, L., T. Y. Chen i C. Leighton. "Spin-dependent band structure effects and measurement of the spin polarization in the candidate half-metalCoS2". Physical Review B 69, nr 9 (16.03.2004). http://dx.doi.org/10.1103/physrevb.69.094412.
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Khanlar, Golnaz, Sahar Izadi Vishkayi i Hamid Rahimpour Soleimani. "The spin-dependent properties of silicon carbide/graphene nanoribbons junctions with vacancy defects". Scientific Reports 11, nr 1 (grudzień 2021). http://dx.doi.org/10.1038/s41598-021-03363-z.
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AbstractWe have designed high-efficient spin-filtering junctions composed of graphene and silicon carbide nanoribbons. We have calculated the spin and charge transport in the junction by non-equilibrium Green’s function formalism combined with the density functional theory to find its spin-dependent electrical conductance, thermal conductance and Seebeck coefficient. In addition, the effect of Si and C atoms vacancies on the transport properties of the junction has been carefully investigated. The enhanced spin-filtering is clearly observed due to the edge and vacancy effects. On the other hand, vacancy defects increase the electrical and spin conductances of the junctions. The results show that the considered junctions are half-metal with reduced thermal conductance which makes them a suitable spin-dependent thermoelectric device. Our results predict the promising potential of the considered junctions for application in spintronic devices.
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Khan, Saba, Yuan Ping Feng i NACIR TIT. "Synergetic effects of combining TM single- and double-atom catalysts embedded in C2N on inducing half-metallicity: DFT study". 2D Materials, 1.12.2022. http://dx.doi.org/10.1088/2053-1583/aca7d4.
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Abstract Designing 2D materials that exhibit half-metallic properties is crucially important in spintronic devices that are used in low-power high-density logic circuits. The large pores in the C2N morphology can stably accommodate various configurations of transition-metal atoms that can lead to ferromagnetic and anti-ferromagnetic coupling interactions amongst them, thus paving the way for achieving half-metallic characteristics. In the present study, we use manganese “Mn” as a promising catalyst and the spin-polarized density-functional theory (DFT) to search for suitable configurations of metal atoms that yield half-metallicity. Test samples comprised of single-atom catalyst (SAC) and double-atom catalyst (DAC) of Mn embedded in a C2N sample of size 2x2 primitive cells (PCs) as well as their combinations in neighboring large pores (i.e., SAC-SAC, SAC-DAC, and DAC-DAC). Tests were extended to screen many other TM catalysts and the results showed the existence of half metallicity in just five cases: (i) C2N:Mn (DAC, SAC-SAC, and SAC-DAC); (ii) C2N:Fe (DAC); and (iii) C2N:Ni (SAC-DAC). Our results further showed the origins of half-metallicity to be attributed to ferromagnetic coupling (FMC) interactions between the catalysts with the 6 mirror images, formed by the periodic-boundary conditions. The FMC interaction is found to have a strength of about 20 meV and a critical length scale up to about ~ 21-29 Å, dependent on both the type of magnetic impurity and the synergetic effects. The potential relevance of half-metallicity to spintronic device application is discussed. Our theoretical results have been benchmarked to the available data in the literature and they were found to be in good agreement.
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Synnatschke, Kevin, Martin Jonak, Alexander Storm, Sourav Laha, Janis Köster, Julian Petry, Steffen Ott i in. "Sonication-assisted liquid exfoliation and size-dependent properties of magnetic two-dimensional α-RuCl3". Journal of Physics D: Applied Physics, 12.04.2023. http://dx.doi.org/10.1088/1361-6463/accc3e.
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Abstract Originating from the hexagonal arrangement of magnetic ions in the presence of strong spin orbit coupling, α-RuCl3 is considered as model system for the Kitaev-Heisenberg model. While the magnetic properties of α-RuCl3 have been studied in bulk single crystals or micromechanically-exfoliated nanosheets, little is known about the nanosheets’ properties after exfoliation by techniques suitable for mass production such as liquid phase exfoliation (LPE). Here, we demonstrate sonication-assisted LPE on α-RuCl3 single crystals in an inert atmosphere. Coupled with centrifugation-based size selection techniques, the accessible size- and thickness range is quantified by statistical atomic force microscopy. Individual nanosheets obtained after centrifugation-based size selection are subjected to transmission electron microscopy to confirm their structural integrity after the exfoliation. The results are combined with bulk characterisation methods, including Raman and X-ray photoelectron spectroscopy, and powder diffraction experiments to evaluate the structural integrity of the nanosheets. We report changes of the magnetic properties of the nanomaterial with nanosheet size, as well as photospectroscopic metrics for the material concentration and average layer number. Finally, a quantitative analysis on environmental effects on the nanomaterial integrity is performed based on time and temperature dependent absorbance spectroscopy revealing a relatively slow decay (half-life of ~2,000 h at 20°C), albeit with low activation energies of 6‑20 kJ/mol.