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Zhang, Chaofan, Yiwei Li, Ding Pei, Zhongkai Liu et Yulin Chen. « Angle-Resolved Photoemission Spectroscopy Study of Topological Quantum Materials ». Annual Review of Materials Research 50, no 1 (1 juillet 2020) : 131–53. http://dx.doi.org/10.1146/annurev-matsci-070218-121852.
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The recently discovered topological quantum materials (TQMs) have electronic structures that can be characterized by certain topological invariants. In these novel materials, the unusual bulk and surface electrons not only give rise to many exotic physical phenomena but also foster potential new technological applications. To characterize the unusual electronic structures of these new materials, investigators have used angle-resolved photoemission spectroscopy (ARPES) as an effective experimental tool to directly visualize the unique bulk and surface electronic structures of TQMs. In this review, we first give a brief introduction of TQMs and ARPES, which is followed by examples of the application of ARPES to different TQMs ranging from topological insulators to Dirac and Weyl semimetals. We conclude with a brief perspective of the current development of ARPES and its potential application in the study of TQMs.
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Bansil, A., R. S. Markiewicz, S. Sahrakorpi, Hsin Lin, M. Lindroos et J. Nieminen. « Modeling electronic structure and highly resolved spectroscopies of cuprates : ARPES, RIXS and STM ». Physica C : Superconductivity and its Applications 460-462 (septembre 2007) : 222–25. http://dx.doi.org/10.1016/j.physc.2007.03.281.
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Radin, Max, et Alexander Kunitsa. « (Invited) Elucidating Redox Mechanisms in Battery Materials through Resonant Inelastic X-Ray Spectroscopy (RIXS) ». ECS Meeting Abstracts MA2024-02, no 26 (22 novembre 2024) : 2085. https://doi.org/10.1149/ma2024-02262085mtgabs.
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Novel battery materials offer the promise of greatly increased energy densities for automative and other applications. However, their practical adoption is often limited by problems in electrochemical performance, such as poor rate capability, voltaic efficiency, and cyclability. Resonant Inelastic X-ray Spectroscopy (RIXS) has become a valuable tool for understanding the redox mechanisms in such materials, representing a first step towards solving problems in electrochemical performance. In many cases, however, the underlying origins of RIXS features are unclear. For example, redox mechanisms in Li-rich cathodes are associated with several absorption and emission features in oxygen RIXS measurements, but a clear picture of what redox mechanisms create these features remains elusive. As a step towards identifying redox mechanisms in Li-rich and related cathode materials, this presentation reviews existing theories of reaction mechanisms in these compounds, revisits experimental RIXS data on these materials and related oxides, and presents ab initio calculations evaluating possible origins of commonly observed features. Results suggest that some features could arise from molecular oxygen residing in low-symmetry environments. Additionally, prospects for using error-corrected quantum computation to more accurately model such electronic structure problems will be discussed.
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Xu, R. Z., X. Gu, W. X. Zhao, J. S. Zhou, Q. Q. Zhang, X. Du, Y. D. Li et al. « Development of a laser-based angle-resolved-photoemission spectrometer with sub-micrometer spatial resolution and high-efficiency spin detection ». Review of Scientific Instruments 94, no 2 (1 février 2023) : 023903. http://dx.doi.org/10.1063/5.0106351.
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Angle-resolved photoemission spectroscopy with sub-micrometer spatial resolution (μ-ARPES), has become a powerful tool for studying quantum materials. To achieve sub-micrometer or even nanometer-scale spatial resolution, it is important to focus the incident light beam (usually from synchrotron radiation) using x-ray optics, such as the zone plate or ellipsoidal capillary mirrors. Recently, we developed a laser-based μ-ARPES with spin-resolution (LMS-ARPES). The 177 nm laser beam is achieved by frequency-doubling a 355 nm beam using a KBBF crystal and subsequently focused using an optical lens with a focal length of about 16 mm. By characterizing the focused spot size using different methods and performing spatial-scanning photoemission measurement, we confirm the sub-micron spatial resolution of the system. Compared with the μ-ARPES facilities based on the synchrotron radiation, our LMS-ARPES system is not only more economical and convenient, but also with higher photon flux (>5 × 1013 photons/s), thus enabling the high-resolution and high-statistics measurements. Moreover, the system is equipped with a two-dimensional spin detector based on exchange scattering at a surface-passivated iron film grown on a W(100) substrate. We investigate the spin structure of the prototype topological insulator Bi2Se3 and reveal a high spin-polarization rate, confirming its spin-momentum locking property. This lab-based LMS-ARPES will be a powerful research tool for studying the local fine electronic structures of different condensed matter systems, including topological quantum materials, mesoscopic materials and structures, and phase-separated materials.
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Chang, Tay-Rong, Qiangsheng Lu, Xiaoxiong Wang, Hsin Lin, T. Miller, Tai-Chang Chiang et Guang Bian. « Band Topology of Bismuth Quantum Films ». Crystals 9, no 10 (30 septembre 2019) : 510. http://dx.doi.org/10.3390/cryst9100510.
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Bismuth has been the key element in the discovery and development of topological insulator materials. Previous theoretical studies indicated that Bi is topologically trivial and it can transform into the topological phase by alloying with Sb. However, recent high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements strongly suggested a topological band structure in pure Bi, conflicting with the theoretical results. To address this issue, we studied the band structure of Bi and Sb films by ARPES and first-principles calculations. The quantum confinement effectively enlarges the energy gap in the band structure of Bi films and enables a direct visualization of the
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topological invariant of Bi. We find that Bi quantum films in topologically trivial and nontrivial phases respond differently to surface perturbations. This way, we establish experimental criteria for detecting the band topology of Bi by spectroscopic methods.
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Cao, Y., D. G. Mazzone, D. Meyers, J. P. Hill, X. Liu, S. Wall et M. P. M. Dean. « Ultrafast dynamics of spin and orbital correlations in quantum materials : an energy- and momentum-resolved perspective ». Philosophical Transactions of the Royal Society A : Mathematical, Physical and Engineering Sciences 377, no 2145 (avril 2019) : 20170480. http://dx.doi.org/10.1098/rsta.2017.0480.
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Many remarkable properties of quantum materials emerge from states with intricate coupling between the charge, spin and orbital degrees of freedom. Ultrafast photo-excitation of these materials holds great promise for understanding and controlling the properties of these states. Here, we introduce time-resolved resonant inelastic X-ray scattering (tr-RIXS) as a means of measuring the charge, spin and orbital excitations out of equilibrium. These excitations encode the correlations and interactions that determine the detailed properties of the states generated. After outlining the basic principles and instrumentations of tr-RIXS, we review our first observations of transient antiferromagnetic correlations in quasi two dimensions in a photo-excited Mott insulator and present possible future routes of this fast-developing technique. The increasing number of X-ray free electron laser facilities not only enables tackling long-standing fundamental scientific problems, but also promises to unleash novel inelastic X-ray scattering spectroscopies. This article is part of the theme issue ‘Measurement of ultrafast electronic and structural dynamics with X-rays’.
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Chaluvadi, Sandeep, Debashis Mondal, Chiara Bigi, Jun Fujii, Rajdeep Adhikari, Regina Ciancio, Alberta Bonanni et al. « Direct-ARPES and STM Investigation of FeSe Thin Film Growth by Nd:YAG Laser ». Coatings 11, no 3 (26 février 2021) : 276. http://dx.doi.org/10.3390/coatings11030276.
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Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe thin films grown by pulsed laser deposition (PLD) on CaF2 (001) substrates as obtained by exploiting the advantages of an all-in-situ ultra-high vacuum (UHV) laboratory allowing for direct high-resolution surface analysis by scanning tunnelling microscopy (STM), synchrotron radiation X-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) on fresh surfaces. FeSe PLD growth protocols were fine-tuned by optimizing target-to-substrate distance d and ablation frequency, atomically flat terraces with unit-cell step heights are obtained, overcoming the spiral morphology often observed by others. In-situ ARPES with linearly polarized horizontal and vertical radiation shows hole-like and electron-like pockets at the Γ and M points of the Fermi surface, consistent with previous observations on cleaved single crystal surfaces. The control achieved in growing quantum materials with volatile elements such as Se by in-situ PLD makes it possible to address the fine analysis of the surfaces by in-situ ARPES and XPS. The study opens wide avenues for the PLD based heterostructures as work-bench for the understanding of proximity-driven effects and for the development of prospective devices based on combinations of quantum materials.
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Kitamura, Miho, Seigo Souma, Asuka Honma, Daisuke Wakabayashi, Hirokazu Tanaka, Akio Toyoshima, Kenta Amemiya et al. « Development of a versatile micro-focused angle-resolved photoemission spectroscopy system with Kirkpatrick–Baez mirror optics ». Review of Scientific Instruments 93, no 3 (1 mars 2022) : 033906. http://dx.doi.org/10.1063/5.0074393.
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Angle-resolved photoemission spectroscopy using a micro-focused beam spot [micro-angle-resolved photoemission spectroscopy (ARPES)] is becoming a powerful tool to elucidate key electronic states of exotic quantum materials. We have developed a versatile micro-ARPES system based on the synchrotron radiation beam focused with a Kirkpatrick–Baez mirror optics. The mirrors are monolithically installed on a stage, which is driven with five-axis motion, and are vibrationally separated from the ARPES measurement system. Spatial mapping of the Au photolithography pattern on Si signifies the beam spot size of 10 µm (horizontal) × 12 µm (vertical) at the sample position, which is well suited to resolve the fine structure in local electronic states. Utilization of the micro-beam and the high precision sample motion system enables the accurate spatially resolved band-structure mapping, as demonstrated by the observation of a small band anomaly associated with tiny sample bending near the edge of a cleaved topological insulator single crystal.
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Nowak, Kamil, Michał Jurczyszyn, Maciej Chrobak, Krzysztof Maćkosz, Andrii Naumov, Natalia Olszowska, Marcin Rosmus et al. « Influence of Doping on the Topological Surface States of Crystalline Bi2Se3 Topological Insulators ». Materials 15, no 6 (11 mars 2022) : 2083. http://dx.doi.org/10.3390/ma15062083.
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We present STM/STS, ARPES and magnetotransport studies of the surface topography and electronic structure of pristine Bi2Se3 in comparison to Bi1.96Mg0.04Se3 and Bi1.98Fe0.02Se3. The topography images reveal a large number of complex, triangle-shaped defects at the surface. The local electronic structure of both the defected and non-defected regions is examined by STS. The defect-related states shift together with the Dirac point observed in the undefected area, suggesting that the local electronic structure at the defects is influenced by doping in the same way as the electronic structure of the undefected surface. Additional information about the electronic structure of the samples is provided by ARPES, which reveals the dependence of the bulk and surface electronic bands on doping, including such parameters as the Fermi wave vector. The subtle changes of the surface electronic structure by doping are verified with magneto-transport measurements at low temperatures (200 mK) allowing the detection of Shubnikov-de Haas (SdH) quantum oscillations.
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Strocov, V. N., F. Lechermann, A. Chikina, F. Alarab, L. L. Lev, V. A. Rogalev, T. Schmitt et M.-A. Husanu. « Dimensionality of mobile electrons at x-ray-irradiated LaAlO3/SrTiO3 interfaces ». Electronic Structure 4, no 1 (4 février 2022) : 015003. http://dx.doi.org/10.1088/2516-1075/ac4e74.
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Abstract Electronic structure of LaAlO3/SrTiO3 (LAO/STO) samples, grown at low oxygen pressure and post-annealed ex situ, was investigated by soft-x-ray ARPES focussing on the Fermi momentum (k F) of the mobile electron system (MES). X-ray irradiation of these samples at temperatures below 100 K creates oxygen vacancies (VOs) injecting Ti t 2g-electrons into the MES. At this temperature the oxygen out-diffusion is suppressed, and the VOs should appear mostly in the top STO layer. The x-ray generated MES demonstrates, however, a pronounced three-dimensional (3D) behavior as evidenced by variations of its experimental k F over different Brillouin zones. Identical to bare STO, this behavior indicates an unexpectedly large extension of the x-ray generated MES into the STO depth. The intrinsic MES in the standard LAO/STO samples annealed in situ, in contrast, demonstrates purely two-dimensional (2D) behaviour. The relevance of our ARPES data analysis is supported by model calculations to compare the intensity vs gradient methods of the k F determination as a function of the energy resolution ratio to the bandwidth. Based on self-interaction-corrected DFT calculations of the MES induced by VOs at the interface and in STO bulk, we discuss possible scenarios of the puzzling 3D-ity. It may involve either a dense ladder of quantum-well states formed in a long-range interfacial potential or, more likely, x-ray-induced bulk metallicity in STO accessed in the ARPES experiment through a short-range interfacial barrier. The mechanism of this metallicity may involve remnant VOs and photoconductivity-induced metallic states in the STO bulk, and even more exotic mechanisms such as x-ray induced formation of Frenkel pairs.
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Shen, Zhi-Xun. « Angle-resolved photoemission spectroscopy (ARPES) : probing electronic structure and many-body interactions ». Coshare Science 2 (23 mai 2024) : 1–43. http://dx.doi.org/10.61109/cs.202405.130.
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Complex phenomenon in quantum materials is a major theme of physics today. As better controlled model systems, a sophisticated understanding of the universality and diversity of these solids may lead to revelations well beyond themselves. Angle-resolved photoemission spectroscopy (ARPES), formulated after Einstein’s photoelectric effect, has been a key tool to uncover the microscopic processes of the electrons that give rise to the rich physics in these solids. Over the last three decades, the improved resolution and carefully matched experiments have been the keys to turn this technique into a leading experimental probe of electronic structures and many-body effects. Drawing upon examples spanning from novel superconductors and topological materials to magnetic and one-dimensional materials, we illustrate ARPES's pivotal role in testing ideas, benchmarking theoretical frameworks, uncovering unexpected phenomena, and elucidating the fingerprints of many-body interactions. Moreover, we demonstrate how the integration of modern ultrafast UV lasers and spin polarimetry has empowered photoemission spectroscopy to capture essential microscopic quantities of electrons—energy, momentum, spin, and temporal dynamics—yielding invaluable insights from a wealth of rich and precise information.
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Villarreal, Renan. « (Invited, Digital Presentation) Single-Atom Quantum Magnetism in 2D Materials ». ECS Meeting Abstracts MA2022-01, no 12 (7 juillet 2022) : 874. http://dx.doi.org/10.1149/ma2022-0112874mtgabs.
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With the advent of 2D materials, the playground to study spins in dilute and non-dilute phases has expanded. This is appealing for utilizing the additional degrees of freedom of electron systems such as spin and valley and, from the fundamental point of view, to better understand atomic scale magnetic phenomena in low dimensional materials. Dilute magnetism in 2D materials can lead to complex magnetic phenomena (e.g., Kondo effect, RKKY-interactions, quantum relaxation and coherence), with potential for applications in spintronics (e.g., spin FETs) and quantum technologies (e.g., single-atom quantum memories). We are investigating how to selectively incorporate substitutional magnetic atoms (3d transition metals and 4f rare earths) in 2D materials, using ultra low energy ion implantation, and we characterize their structural, electronic, and magnetic properties [1]. Ultra-low energy (ULE) ion implantation allows us to precisely tune the kinetic energy of the ions, providing control over the form of incorporation and concentration while preserving the structural and electronic properties of graphene. Our approach is based on a wide range of characterization techniques (structural and electronic), including scanning tunneling microscopy and spectroscopy (STM/STS), Raman spectroscopy, synchrotron-based X-ray photoelectron spectroscopy (XPS), angle-resolved photoemission spectroscopy (ARPES), X-ray magnetic circular dichroism (XMCD), among others. These experimental studies are complemented by density functional theory (DFT) and molecular dynamics (MD) simulations. The new insights provided by our work establish a framework for the controlled incorporation of magnetic dopants in 2D materials, using ULE ion implantation. [1] P. C. Lin et al., ACS Nano 15(3), 5449-5458 (2021).
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Bouravleuv, A. D., L. L. Lev, C. Piamonteze, X. Wang, T. Schmitt, A. I. Khrebtov, Yu B. Samsonenko, J. Kanski, G. E. Cirlin et V. N. Strocov. « Electronic structure of (In,Mn)As quantum dots buried in GaAs investigated by soft-x-ray ARPES ». Nanotechnology 27, no 42 (15 septembre 2016) : 425706. http://dx.doi.org/10.1088/0957-4484/27/42/425706.
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Na, M. X., A. K. Mills, F. Boschini, M. Michiardi, B. Nosarzewski, R. P. Day, E. Razzoli et al. « Direct determination of mode-projected electron-phonon coupling in the time domain ». Science 366, no 6470 (5 décembre 2019) : 1231–36. http://dx.doi.org/10.1126/science.aaw1662.
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Ultrafast spectroscopies have become an important tool for elucidating the microscopic description and dynamical properties of quantum materials. In particular, by tracking the dynamics of nonthermal electrons, a material’s dominant scattering processes can be revealed. Here, we present a method for extracting the electron-phonon coupling strength in the time domain, using time- and angle-resolved photoemission spectroscopy (TR-ARPES). This method is demonstrated in graphite, where we investigate the dynamics of photoinjected electrons at the K¯ point, detecting quantized energy-loss processes that correspond to the emission of strongly coupled optical phonons. We show that the observed characteristic time scale for spectral weight transfer mediated by phonon-scattering processes allows for the direct quantitative extraction of electron-phonon matrix elements for specific modes.
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Bigi, Chiara, Pranab K. Das, Davide Benedetti, Federico Salvador, Damjan Krizmancic, Rudi Sergo, Andrea Martin et al. « Very efficient spin polarization analysis (VESPA) : new exchange scattering-based setup for spin-resolved ARPES at APE-NFFA beamline at Elettra ». Journal of Synchrotron Radiation 24, no 4 (13 juin 2017) : 750–56. http://dx.doi.org/10.1107/s1600577517006907.
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Complete photoemission experiments, enabling measurement of the full quantum set of the photoelectron final state, are in high demand for studying materials and nanostructures whose properties are determined by strong electron and spin correlations. Here the implementation of the new spin polarimeter VESPA (Very Efficient Spin Polarization Analysis) at the APE-NFFA beamline at Elettra is reported, which is based on the exchange coupling between the photoelectron spin and a ferromagnetic surface in a reflectometry setup. The system was designed to be integrated with a dedicated Scienta-Omicron DA30 electron energy analyzer allowing for two simultaneous reflectometry measurements, along perpendicular axes, that, after magnetization switching of the two targets, allow the three-dimensional vectorial reconstruction of the spin polarization to be performed while operating the DA30 in high-resolution mode. VESPA represents the very first installation for spin-resolved ARPES (SPARPES) at the Elettra synchrotron in Trieste, and is being heavily exploited by SPARPES users since autumn 2015.
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Nilforoushan, Niloufar, Michele Casula, Adriano Amaricci, Marco Caputo, Jonathan Caillaux, Lama Khalil, Evangelos Papalazarou et al. « Moving Dirac nodes by chemical substitution ». Proceedings of the National Academy of Sciences 118, no 33 (12 août 2021) : e2108617118. http://dx.doi.org/10.1073/pnas.2108617118.
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Dirac fermions play a central role in the study of topological phases, for they can generate a variety of exotic states, such as Weyl semimetals and topological insulators. The control and manipulation of Dirac fermions constitute a fundamental step toward the realization of novel concepts of electronic devices and quantum computation. By means of Angle-Resolved Photo-Emission Spectroscopy (ARPES) experiments and ab initio simulations, here, we show that Dirac states can be effectively tuned by doping a transition metal sulfide, BaNiS2, through Co/Ni substitution. The symmetry and chemical characteristics of this material, combined with the modification of the charge-transfer gap of BaCo1−xNixS2 across its phase diagram, lead to the formation of Dirac lines, whose position in k-space can be displaced along the Γ−M symmetry direction and their form reshaped. Not only does the doping x tailor the location and shape of the Dirac bands, but it also controls the metal-insulator transition in the same compound, making BaCo1−xNixS2 a model system to functionalize Dirac materials by varying the strength of electron correlations.
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Su, Shu-Hsuan, Jen-Te Chang, Pei-Yu Chuang, Ming-Chieh Tsai, Yu-Wei Peng, Min Kai Lee, Cheng-Maw Cheng et Jung-Chung Andrew Huang. « Epitaxial Growth and Structural Characterizations of MnBi2Te4 Thin Films in Nanoscale ». Nanomaterials 11, no 12 (7 décembre 2021) : 3322. http://dx.doi.org/10.3390/nano11123322.
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The intrinsic magnetic topological insulator MnBi2Te4 has attracted much attention due to its special magnetic and topological properties. To date, most reports have focused on bulk or flake samples. For material integration and device applications, the epitaxial growth of MnBi2Te4 film in nanoscale is more important but challenging. Here, we report the growth of self-regulated MnBi2Te4 films by the molecular beam epitaxy. By tuning the substrate temperature to the optimal temperature for the growth surface, the stoichiometry of MnBi2Te4 becomes sensitive to the Mn/Bi flux ratio. Excessive and deficient Mn resulted in the formation of a MnTe and Bi2Te3 phase, respectively. The magnetic measurement of the 7 SL MnBi2Te4 film probed by the superconducting quantum interference device (SQUID) shows that the antiferromagnetic order occurring at the Néel temperature 22 K is accompanied by an anomalous magnetic hysteresis loop along the c-axis. The band structure measured by angle-resolved photoemission spectroscopy (ARPES) at 80 K reveals a Dirac-like surface state, which indicates that MnBi2Te4 has topological insulator properties in the paramagnetic phase. Our work demonstrates the key growth parameters for the design and optimization of the synthesis of nanoscale MnBi2Te4 films, which are of great significance for fundamental research and device applications involving antiferromagnetic topological insulators.
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Meng, Qinghao, Fan Yu, Gan Liu, Junyu Zong, Qichao Tian, Kaili Wang, Xiaodong Qiu, Can Wang, Xiaoxiang Xi et Yi Zhang. « Thickness-Dependent Evolutions of Surface Reconstruction and Band Structures in Epitaxial β–In2Se3 Thin Films ». Nanomaterials 13, no 9 (3 mai 2023) : 1533. http://dx.doi.org/10.3390/nano13091533.
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Ferroelectric materials have received great attention in the field of data storage, benefiting from their exotic transport properties. Among these materials, the two-dimensional (2D) In2Se3 has been of particular interest because of its ability to exhibit both in-plane and out-of-plane ferroelectricity. In this article, we realized the molecular beam epitaxial (MBE) growth of β–In2Se3 films on bilayer graphene (BLG) substrates with precisely controlled thickness. Combining in situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) measurements, we found that the four-monolayer β–In2Se3 is a semiconductor with a (9 × 1) reconstructed superlattice. In contrast, the monolayer β–In2Se3/BLG heterostructure does not show any surface reconstruction due to the interfacial interaction and moiré superlattice, which instead results in a folding Dirac cone at the center of the Brillouin zone. In addition, we found that the band gap of In2Se3 film decreases after potassium doping on its surface, and the valence band maximum also shifts in momentum after surface potassium doping. The successful growth of high-quality β–In2Se3 thin films would be a new platform for studying the 2D ferroelectric heterostructures and devices. The experimental results on the surface reconstruction and band structures also provide important information on the quantum confinement and interfacial effects in the epitaxial β–In2Se3 films.
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Merckling, Clement, Islam Ahmed, Tsang Hsuan Tsang, Moloud Kaviani, Jan Genoe et Stefan De Gendt. « (Invited) Integrated Perovskites Oxides on Silicon : From Optical to Quantum Applications ». ECS Meeting Abstracts MA2022-01, no 19 (7 juillet 2022) : 1060. http://dx.doi.org/10.1149/ma2022-01191060mtgabs.
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With the slowing down of Moore’s law, related to conventional scaling of integrated circuits, alternative technologies will require research effort for pushing the limits of new generations of electronic or photonic devices. Perovskite oxides with the ABO3 chemical formula have a very wide range of interesting intrinsic properties such as metal-insulator transition, ferroelectricity, pyroelectricity, piezoelectricity, ferromagnetic and superconductivity. For the integration of such oxides, it is of great interest to combine their properties with traditional electronic, memory and optical devices on the same silicon-based platform. In the context of high-speed chip-to-chip optical interconnects, compact high-resolution beam steering and video-rate RGB hologram generation require the integration of fast and efficient optical modulators on top of silicon CMOS devices. For these applications the integration of high quality electro-optical materials A defect-free material-stack deposition on silicon wafers is hence required. Among the possible materials options, barium titanate (BaTiO3) is one promising candidate due to its large intrinsic Pockels coefficients that can be obtained. In a first part of the talk, we will review the different options to integrate BaTiO3 on Silicon substrate though different templates to control the polarization direction and discuss the influence on the physical, electrical and optical properties. Then in the second section we will discuss the use of perovskites oxide in the field of topological based qubits which is one of the promising methods for realizing fault-tolerant computations. It is recognized that superconductor/topological insulator heterostructure interfaces may be a perfect host for the exotic “Majorana” particles. These have relevant topological protection nature as required for processing information. Therefore, the physics at the superconductor/topological insulator heterostructure interface need to be studied further, starting at the material level. In this work, a candidate material Barium Bismuthate (BBO) is studied utilizing the Oxide Molecular Beam Epitaxy (MBE) process. The perovskite structure provides opportunity for easily tailored functionality through substitutional doping. Incorporation of potassium into the lattice of BBO results in a superconducting phase with Curie temperature as high as ~ 30K. In addition, BBO is according to DFT based studies, predicted to form topological surface states when doped with Fluorine. In our work, we integrate BBO perovskite on Si(001) substrate, using an epitaxially grown strontium titanate (STO) single-crystalline buffer layer and discuss the structural and chemical properties of the heterostructure will be established by utilizing physical characterization techniques such as AFM, and TEM in later stages. This will go hand in hand with the understanding of the ARPES studies and related surface reconstruction of BBO observed by RHEED as a criterion for the high-quality films. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant agreements No 864483 and 742299)”.
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John, Ataman Ose, Molua Ogom Collins et Vwavware Oruaode Jude. « Electronic Band Structure of Heavy Fermion Compound Cecoge2 ». Journal of Energy Engineering and Thermodynamics, no 36 (18 septembre 2023) : 22–31. http://dx.doi.org/10.55529/jeet.36.22.31.
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The following article provides a thorough examination of the electronic band structure observed in heavy fermion compounds, which are a type of material that has received considerable interest within the realm of condensed matter physics. The compounds under consideration exhibit significantly high charge carrier masses, which give rise to intriguing electronic phenomena when subjected to low temperatures. Through the analysis of electronic band structures, valuable insights can be obtained regarding the distinctive characteristics displayed by these captivating materials. The research centers on the distinctive attributes and theoretical frameworks employed to elucidate the electronic properties of the subjects under investigation. In this study, we present an introduction to heavy fermions and their experimental manifestations, including the observation of enhanced specific heat and low-temperature resistivity. The present study delves into the theoretical examination of the Kondo effect, which involves the emergence of heavy quasi-particles resulting from the hybridization process between localized f-electrons and conduction electrons. This paper examines the utilization of band structure calculations and various spectroscopic techniques, including angle-resolved photoemission spectroscopy (ARPES), inelastic neutron scattering, and transport measurements. The experimental results demonstrate the presence of hybridization gaps, the characteristics of the Fermi surface topology, and the occurrence of spin fluctuations. This study investigates the effects of crystal symmetry, spin-orbit coupling, and external perturbations on the electronic band structure. Specifically, it explores how these factors influence hybridization strength, Fermi surface topology, and quantum phase transitions. The abstract provides a concise overview of the existing knowledge, acknowledges the obstacles encountered, and proposes potential avenues for further investigation. The significance of this research lies in its ability to elucidate the fundamental principles of heavy fermion compounds, as well as explore their potential practical implications.
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Yinpeng Zhong, Jiatai Feng et Xia Yang. « Advances in Free-Electron-Laser based scattering techniques and spectroscopic methods ». Acta Physica Sinica, 2024, 0. http://dx.doi.org/10.7498/aps.73.20240930.
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In 2005, the FLASH soft X-ray free-electron laser (FEL) in Hamburg, Germany, achieved its first lasing, marking the beginning of an intensive phase of global FEL construction. Subsequently, the United States, Japan, South Korea, China, Italy, and Switzerland have all commenced building this type of photon facility. Recently, the new generation of FEL has started to utilize superconducting acceleration technology to achieve high-repetition-rate pulse output, thereby improving experimental efficiency. Currently completed facilities include the European XFEL, with ongoing constructions of the LCLS-II in the United States and the SHINE facility in Shanghai. The Shenzhen Superconducting soft X-ray Free-electron Laser (S<sup>3</sup>FEL) is also in preparation.<br>These FEL facilities generate coherent and tunable ultrashort pulses across the extreme ultraviolet to hard X-ray spectrum, advancing FEL-based scattering techniques such as ultrafast X-ray scattering, spectroscopy, and X-ray nonlinear optics, thereby transforming the way we study correlated quantum materials at ultrafast timescales.<br>The Self-Amplified Spontaneous Emission (SASE) process in FEL leads to timing jitter between FEL pulses and the synchronized pump laser, impacting the accuracy of ultrafast time-resolved measurements. To address this issue, timing tools have been developed to measure these jitters and reindex each pump-probe signal after measurement. This success enables ultrafast X-ray diffraction (UXRD) to be first realized, a systematic study of Peierls distorted materials is demonstrated. Furthermore, the high flux of FEL pulses enable Fourier Transform Inelastic X-ray Scattering (FT-IXS) method, which allows the extraction the phonon dispersion curves throughout the entire Brillouin zone by applying the Fourier transform to the measured momentum dependent coherent phonon scattering signals, even when the system is in a non-equilibrium state.<br>UXRD is typically employed to study ultrafast lattice dynamics, which requires hard X-ray wavelengths. In contrast, time resolved resonant elastic X-ray scattering (tr-REXS) in the soft X-ray regime has become a standard method for investigating nano-sized charge and spin orders in correlated quantum materials at ultrafast time scales.<br>In correlated quantum materials, the interplay between electron and lattice dynamics represents another important research direction. In addition to Zhi-Xun Shen's successful demonstration of the combined tr-ARPES and UXRD method at SLAC, this paper also reports attempts to integrate UXRD with Resonant X-ray Emission Spectroscopy (RXES) for the simultaneous measurement of electronic and lattice dynamics.<br>Resonant Inelastic X-ray Scattering (RIXS) is a powerful tool for studying elementary and collective excitations in correlated quantum materials. However, in FEL-based soft X-ray spectroscopy, the wavefront tilt introduced by the widely used grating monochromators inevitably stretches the FEL pulses, which degrades the time resolution. Therefore, the new design at FEL beamlines employs low line density gratings with long exit arms to reduce pulse stretch and achieve relatively high energy resolution. For example, the Heisenberg-RIXS instrument at the European XFEL achieves an energy resolution of 92 meV at the Cu L<sub>3</sub> edge and approximately 150 fs time resolution.<br>In recent years, scientists at SwissFEL's Furka station have drawn inspiration from femtosecond optical covariance spectroscopy to propose a new method for generating two-dimensional time-resolved Resonant Inelastic X-ray Scattering (2D tr-RIXS) spectra. This method involves real-time detection of single-shot FEL incident and scattered spectra, followed by deconvolution calculation to avoid photon waste and wavefront tilt caused by monochromator slits. The SQS experimental station at European XFEL, in 2023, features a 1D-XUV spectrometer that utilizes subtle variations in photon energy absorption across the sample to induce spatial energy dispersion. Using Wolter mirrors, it directly images spatially resolved fluorescence emission from the sample onto the detector to generate 2D tr-RIXS spectra without the need for deconvolution. However, this design is limited to specific samples. Currently, the S3FEL is designing a novel 2D tr-RIXS instrument that uses an upstream low line density grating monochromator to generate spatial dispersion of the beam spot, allowing the full bandwidth of SASE to project spatially dispersed photon energy onto the sample. Subsequently, a similar optical design to the 1D-XUV spectrometer will be employed to achieve two-dimensional tr-RIXS spectra, thereby expanding the applicability beyond specific liquid samples. These new instruments are designed to minimize pulse elongation by fully utilizing SASE's full bandwidth, approaching Fourier-transform-limited RIXS spectra in both time and energy resolution.<br>Nonlinear X-ray optics techniques such as sum-frequency generation (SFG) and second-harmonic generation are being adapted for X-ray wavelengths, opening new avenues for probing elementary excitations. X-ray transient grating spectroscopy extends capabilities to study charge transport and spin dynamics on ultrafast timescales. The future developing of these scattering methods offer unique opportunities for probing dynamical events in a wide variety of systems, including surface and interface processes, chirality, nanoscale transport and the termed as multidimensional core-level spectroscopy.
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Zhou Ke-Jin. « Resonant Inelastic X-ray Scattering Applications in Quantum Materials ». Acta Physica Sinica, 2024, 0. http://dx.doi.org/10.7498/aps.73.20241009.
Texte intégralRésumé :
The essence of quantum materials lies in the intricate coupling among charge, spin, orbital and lattice degrees of freedom. Although X-ray photoemission spectroscopy and inelastic neutron scattering are advantegous in detecting fermionic single-particle spectral function and bosonic spin excitations in quantum materials, respectively, probing other bosonic collective excitations especially their coupling is not possible until the establishment of the advanced resonant inelastic X-ray scattering (RIXS). In the past decades, RIXS has flourished with continuously improved energy resolution which made a paradigm shift from measuring crystal-field splitting and the charge-transfer excitation, to probe collective excitations and the order parameters of all degrees of freedom. This review article summarises the most recent progress made by the soft X-ray RIXS in the field of quantum materials. For instance, three-dimensional collective charge excitations, plasmons, were discovered experimentally by RIXS in both electron and hole doped cuprate superconductors. The collective orbital excitations and excitons were found in copper and nickel based quantum materials. For the newly discovered nickelate superconductors, RIXS has made substantial contributions in characterising their electronic and magnetic excitations and the related ordering phenomena critical for an in-depth understanding of the underlying superconducting mechanicsm. RIXS is a unique tool in probing the higher-order spin excitations in quantum materials thanks to the strong spin-orbit coupling and the core-valence exchange interaction. RIXS is also found superior in probing the Stoner magnetic excitations in magnetic metals and topological magnetic materials. Finally, a short perspective is provided in terms of the development of RIXS technique in Chinese large-scale research facilities.
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Andresen, Nord, Christos Bakalis, Peter Denes, Azriel Goldschmidt, Ian Johnson, John M. Joseph, Armin Karcher, Amanda Krieger et Craig Tindall. « A low noise CMOS camera system for 2D resonant inelastic soft X-ray scattering ». Frontiers in Physics 11 (20 novembre 2023). http://dx.doi.org/10.3389/fphy.2023.1285379.
Texte intégralRésumé :
Resonant Inelastic X-ray Scattering (RIXS) is a powerful spectroscopic technique to study quantum properties of materials in the bulk. A novel variant of RIXS, called 2D RIXS, enables concurrent measurement of the scattered X-ray spectrum for a wide range of input energies, improving on the typically low throughput of 1D RIXS. In the soft X-ray domain, 2D RIXS demands an X-ray camera system with small pixels, large area, high quantum efficiency and low noise to limit the false detection rate in long duration exposures. We designed and implemented a 7.5 Megapixel back-illuminated CMOS detector with 5 μm pixels and high quantum efficiency in the 200–1,000 eV X-ray energy range for the QERLIN 2D RIXS spectrometer at the Advanced Light Source. The QERLIN beamline and detector are currently in commissioning. The camera noise from in-situ 3 s long dark exposures is 7e− or less and the leakage current is 6.5 × 10−3 e−/(pixel ∙ s). For individual 500 eV X-rays, the expected efficiency is greater than 75% and the false detection rate is ∼1 × 10−5 per pixel.
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Mitrano, M., S. Johnston, Young-June Kim et M. P. M. Dean. « Exploring Quantum Materials with Resonant Inelastic X-Ray Scattering ». Physical Review X 14, no 4 (13 décembre 2024). https://doi.org/10.1103/physrevx.14.040501.
Texte intégralRésumé :
Understanding quantum materials—solids in which interactions among constituent electrons yield a great variety of novel emergent quantum phenomena—is a forefront challenge in modern condensed matter physics. This goal has driven the invention and refinement of several experimental methods, which can spectroscopically determine the elementary excitations and correlation functions that determine material properties. Here we focus on the future experimental and theoretical trends of resonant inelastic x-ray scattering (RIXS), which is a remarkably versatile and rapidly growing technique for probing different charge, lattice, spin, and orbital excitations in quantum materials. We provide a forward-looking introduction to RIXS and outline how this technique is poised to deepen our insight into the nature of quantum materials and of their emergent electronic phenomena. Published by the American Physical Society 2024
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Boschini, Fabio, Marta Zonno et Andrea Damascelli. « Time-resolved ARPES studies of quantum materials ». Reviews of Modern Physics 96, no 1 (27 février 2024). http://dx.doi.org/10.1103/revmodphys.96.015003.
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Huang, Jianwei, Ziqin Yue, Andrey Baydin, Hanyu Zhu, Hiroyuki Nojiri, Junichiro Kono, Yu He et Ming Yi. « Angle-resolved photoemission spectroscopy with an in situ tunable magnetic field ». Review of Scientific Instruments 94, no 9 (1 septembre 2023). http://dx.doi.org/10.1063/5.0157031.
Texte intégralRésumé :
Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool for probing the momentum-resolved single-particle spectral function of materials. Historically, in situ magnetic fields have been carefully avoided as they are detrimental to the control of photoelectron trajectory during the photoelectron detection process. However, magnetic field is an important experimental knob for both probing and tuning symmetry-breaking phases and electronic topology in quantum materials. In this paper, we introduce an easily implementable method for realizing an in situ tunable magnetic field at the sample position in an ARPES experiment and analyze magnetic-field-induced artifacts in the ARPES data. Specifically, we identified and quantified three distinct extrinsic effects of a magnetic field: constant energy contour rotation, emission angle contraction, and momentum broadening. We examined these effects in three prototypical quantum materials, i.e., a topological insulator (Bi2Se3), an iron-based superconductor (LiFeAs), and a cuprate superconductor (Pb-Bi2Sr2CuO6+x), and demonstrate the feasibility of ARPES measurements in the presence of a controllable magnetic field. Our studies lay the foundation for the future development of the technique and interpretation of ARPES measurements of field-tunable quantum phases.
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Wang, Yang, et Maciej Dendzik. « Recent Progress in Angle-resolved Photoemission Spectroscopy ». Measurement Science and Technology, 27 décembre 2023. http://dx.doi.org/10.1088/1361-6501/ad1915.
Texte intégralRésumé :
Abstract Angle-resolved photoemission spectroscopy (ARPES) is a well-established experimental technique that allows probing of the electronic structure of quantum materials using relatively high-energy photons. ARPES has been extensively used to study important classes of materials such as topological insulators, high-temperature superconductors, two-dimensional materials or interface systems. Although the technique was originally developed over 60 years ago, the last decade has witnessed significant advancements in instrumentation. In this review, we survey recent progress in ARPES, with a focus on developments in novel light sources and electron detection methods, which enable the expansion of ARPES into spin-, time-, or space-resolved domains. Important examples of ARPES results are presented, together with an outlook for the field.
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Lim, Chan-young, Sunghun Kim, Sung Won Jung, Jinwoong Hwang et Yeongkwan Kim. « Recent Technical Advancements in ARPES : Unveiling Quantum Materials ». Current Applied Physics, février 2024. http://dx.doi.org/10.1016/j.cap.2024.01.010.
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Schüler, Michael, Thorsten Schmitt et Philipp Werner. « Probing magnetic orbitals and Berry curvature with circular dichroism in resonant inelastic X-ray scattering ». npj Quantum Materials 8, no 1 (19 janvier 2023). http://dx.doi.org/10.1038/s41535-023-00538-x.
Texte intégralRésumé :
AbstractResonant inelastic X-ray scattering (RIXS) can probe localized excitations at selected atoms in materials, including particle-hole transitions between the valence and conduction bands. These transitions are governed by fundamental properties of the corresponding Bloch wave functions, including orbital and magnetic degrees of freedom, and quantum geometric properties such as the Berry curvature. In particular, orbital angular momentum (OAM), which is closely linked to the Berry curvature, can exhibit a nontrivial momentum dependence. We demonstrate how information on such OAM textures can be extracted from the circular dichroism in RIXS. Based on accurate modeling with a first-principles treatment of the key ingredient—the light–matter interaction—we simulate dichroic RIXS spectra for the prototypical transition-metal dichalcogenide MoSe2 and the two-dimensional topological insulator 1T$${}^{{\prime}}$$ ′ -MoS2. Guided by an intuitive picture of the optical selection rules, we discuss how the momentum-dependent OAM manifests itself in the dichroic RIXS signal if one controls the momentum transfer. Our calculations are performed for typical experimental geometries and parameter regimes, and demonstrate the possibility of observing the predicted circular dichroism in forthcoming experiments. Thus, our work establishes a new avenue for observing Berry curvature and topological states in quantum materials.
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Balduini, F., L. Rocchino, A. Molinari, T. Paul, G. Mariani, V. Hasse, C. Felser, C. Zota, H. Schmid et B. Gotsmann. « Probing the Shape of the Weyl Fermi Surface of NbP Using Transverse Electron Focusing ». Physical Review Letters 133, no 9 (28 août 2024). http://dx.doi.org/10.1103/physrevlett.133.096601.
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Weyl semimetals are defined by their unique Fermi surface, comprising pairs of Weyl points of opposite chirality, connected through topological surface states. Angle-resolved photoemission spectroscopy (ARPES) has been used to verify the existence of the Weyl points and the Fermi arcs. However, ARPES is limited in resolution, leading to significant uncertainty when characterizing the shape of the Fermi surface of semimetals and measuring features such as the distance between the Weyl points. Here, to surpass the resolution of ARPES, we combine quantum oscillation measurements with transverse electron focusing experiments. These techniques offer complementary information, enabling the reconstruction of the distinctive peanut-shaped cross section of the Weyl Fermi surface and accurately determining the separation between Weyl points in the Weyl semimetal NbP. Our Letter showcases the integration of quantum oscillations and transverse electron focusing, allowing for the measurements of complex Fermi surface geometries, concurrently with carriers’ transport properties, in high-mobility quantum materials. Published by the American Physical Society 2024
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Jiang, Zhicheng, Jiayu Liu, Zhengtai Liu et Dawei Shen. « A review of angle-resolved photoemission spectroscopy study on topological mangetic material family of MnBi2Te4 ». Electronic Structure, 13 décembre 2022. http://dx.doi.org/10.1088/2516-1075/acab47.
Texte intégralRésumé :
Abstract The MnBi2Te4 family compounds have drawn enormous attention in recent years due to their potential to realize the high-temperature quantum anomalous Hall effect (QAHE). As one of the most direct techniques to probe electronic structure, angle-resolved photoemission spectroscopy (ARPES) has been widely applied to investigate the interplay between the magnetism and non-trivial topological band structure of MnBi2Te4 family materials. Here, we briefly review some of latest progress of ARPES on MnBi2Te4·(Bi2Te3) (n=0, 1, 2, 3) and analogous MnSb2Te4·(Sb2Te3) (n=1,2) series of materials. Aside from the direct observation of the non-trivial topological band structure, ARPES results reveal that their surface band gap can be well modulated by both temperature and Bi2Te3 interpolation. In addition, although ARPES results of the topological surface states are still under hot debate, the extensive experimental results have provided an opportunity to shed light on the complex interactions in MnBi2Te4 family materials.
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Cai, Yongqing, Yuan Wang, Zhanyang Hao, Yixuan Liu, Xuelei Sui, Zuowei Liang, Xiao-Ming Ma et al. « Emergence of quantum confinement in topological kagome superconductor CsV3Sb5 ». Communications Materials 5, no 1 (13 mars 2024). http://dx.doi.org/10.1038/s43246-024-00461-z.
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AbstractQuantum confinement is a restriction on the motion of electrons in a material to specific region, resulting in discrete energy levels rather than continuous energy bands. In certain materials, quantum confinement could dramatically reshape the electronic structure and properties of the surface with respect to the bulk. Here, in the recently discovered kagome superconductors CsV3Sb5, we unveil the dominant role of quantum confinement in determining their surface electronic structure. Combining angle-resolved photoemission spectroscopy (ARPES) measurement and density-functional theory simulation, we report the observations of two-dimensional quantum well states due to the confinement of bulk electron pocket and Dirac cone to the nearly isolated surface layer. The theoretical calculations on the slab model also suggest that the ARPES observed spectra are almost entirely contributed by the top two layers. Our results not only explain the disagreement of band structures between the recent experiments and calculations, but also suggest an equally important role played by quantum confinement, together with strong correlation and band topology, in shaping the electronic properties of this material.
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Iwasawa, Hideaki, Tetsuro Ueno, Takahiko Masui et Setsuko Tajima. « Unsupervised clustering for identifying spatial inhomogeneity on local electronic structures ». npj Quantum Materials 7, no 1 (18 février 2022). http://dx.doi.org/10.1038/s41535-021-00407-5.
Texte intégralRésumé :
AbstractSpatial inhomogeneity on the electronic structure is one of the vital keys to provide a better understanding of the emergent quantum phenomenon. Given the recent developments on spatially resolved ARPES (ARPES: angle-resolved photoemission spectroscopy), the information on the spatial inhomogeneity on the local electronic structure is now accessible. However, the next challenge becomes apparent as the conventional analysis encounters difficulty handling a large volume of a spatial mapping dataset, typically generated in the spatially resolved ARPES experiments. Here, we propose a machine-learning-based approach using unsupervised clustering algorithms (K-means and fuzzy-c-means) to examine the spatial mapping dataset. Our analysis methods enable automated categorization of the spatial mapping dataset with a much-reduced human intervention and workload, thereby allowing quick identification and visualization of the spatial inhomogeneity on the local electronic structures.
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He, Yu, Frederick J. Walker, Charles H. Ahn et Sohrab Ismail‐Beigi. « Probing the Wannier function of Crystalline Solids with Angle‐Resolved Photoemission Spectroscopy ». Advanced Materials Interfaces, 25 août 2024. http://dx.doi.org/10.1002/admi.202400427.
Texte intégralRésumé :
AbstractAngle‐resolved photoemission spectroscopy (ARPES) has been a widely adopted technique in the studies of quantum materials. The surface sensitivity of photoelectric effect also makes it a powerful tool to investigate surface and shallow interface phenomena. While an overwhelming majority of its use focuses on extracting the eigenenergy of the electron Bloch states in momentum space, attempts to extract information of the wave function via ARPES has been limited to molecular systems. In this perspective, it is proposed and advocated use ARPES to investigate and unravel wave function properties, as opposed to only the electron energy‐momentum dispersion relation, in crystalline solids and their interfaces. This can help enhance the rapidly growing development of material properties based on the spatial and geometric properties of the electronic wave functions.
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Li, Yiwei, Qiang Wan et Nan Xu. « Recent Advances in Moiré Superlattice Systems by Angle‐Resolved Photoemission Spectroscopy ». Advanced Materials, 9 septembre 2023. http://dx.doi.org/10.1002/adma.202305175.
Texte intégralRésumé :
AbstractThe last decade has witnessed a flourish in two‐dimensional (2D) materials including graphene and transition metal dichalcogenides (TMDs) as atomic‐scale Legos. Artificial moiré superlattices via stacking 2D materials with a twist angle and/or a lattice mismatch have recently become a fertile playground exhibiting a plethora of emergent properties beyond their building blocks. These rich quantum phenomena stem from their nontrivial electronic structures that have been effectively tuned by the moiré periodicity. Modern angle‐resolved photoemission spectroscopy (ARPES) can directly visualize electronic structures with decent momentum, energy, and spatial resolution, thus could provide enlightening insights into fundamental physics in moiré superlattice systems and guides for designing novel devices. In this review, firstly a brief introduction is given on advanced ARPES techniques and basic ideas of band structures in a moiré superlattice system. Then ARPES research results of various moiré superlattice systems are highlighted, including graphene on substrates with small lattice mismatches, twisted graphene/TMD moiré systems, and high‐order moiré superlattice systems. Finally, we discuss on important questions that remain open, challenges in current experimental investigations and present an outlook on this field of research.This article is protected by copyright. All rights reserved
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Pelliciari, Jonathan, Kenji Ishii, Yaobo Huang, Marcus Dantz, Xingye Lu, Paul Olalde-Velasco, Vladimir N. Strocov et al. « Reciprocity between local moments and collective magnetic excitations in the phase diagram of BaFe2(As1−xPx)2 ». Communications Physics 2, no 1 (7 novembre 2019). http://dx.doi.org/10.1038/s42005-019-0236-3.
Texte intégralRésumé :
Abstract Unconventional superconductivity arises at the border between the strong coupling regime with local magnetic moments and the weak coupling regime with itinerant electrons, and stems from the physics of criticality that dissects the two. Unveiling the nature of the quasiparticles close to quantum criticality is fundamental to understand the phase diagram of quantum materials. Here, using resonant inelastic x-ray scattering (RIXS) and $${\rm{Fe}}-{{\rm{K}}}_{\beta }$$ Fe − K β emission spectroscopy (XES), we visualize the coexistence and evolution of local magnetic moments and collective spin excitations across the superconducting dome in isovalently-doped BaFe$${}_{2}$$ 2 (As$${}_{1-x}$$ 1 − x P$${}_{x}$$ x )$${}_{2}$$ 2 (0.00 $$ \le $$ ≤ x $$\le 0.52$$ ≤ 0.52 ). Collective magnetic excitations resolved by RIXS are gradually hardened, whereas XES reveals a strong suppression of the local magnetic moment upon doping. This relationship is captured by an intermediate coupling theory, explicitly accounting for the partially localized and itinerant nature of the electrons in Fe pnictides. Finally, our work identifies a local-itinerant spin fluctuations channel through which the local moments transfer spin excitations to the particle-hole (paramagnons) continuum across the superconducting dome.
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Wong, Deniz Po, Christian Schulz et Maciej Bartkowiak. « PEAXIS : A RIXS and XPS Endstation for Solid-State Quantum and Energy Materials at BESSY II ». Journal of large-scale research facilities JLSRF 7 (8 juillet 2021). http://dx.doi.org/10.17815/jlsrf-7-177.
Texte intégralRésumé :
PEAXIS (Photo Electron Analysis and resonant X-ray Inelastic Spectroscopy) is a dedicated endstation installed at the beamline U41-PEAXIS that offers high resolution soft X-ray spectroscopy measurements with incident photon energies ranging from 180 – 1600 eV. The endstation combines two X-ray spectroscopic techniques, X-ray photoelectron spectroscopy (XPS) and resonant inelastic soft X-ray scattering (RIXS), which are important for probing the electronic structure and local and collective excitations of solid-state materials. It features a continuous variation of scattering angle under UHV conditions for wave vector-resolved studies and a modular sample environment that allows investigation in the temperature range between 10 K and 1000 K.
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Lu, Shengyue, Yeqinbo Zhang, Jingze Li, Xueyan Ma, Yongkai Deng et Yunquan Liu. « A newly designed laser-based time- and angle-resolved photoelectron spectroscopy with a time-of-flight electron analyzer ». AIP Advances 15, no 1 (1 janvier 2025). https://doi.org/10.1063/5.0230542.
Texte intégralRésumé :
Angle-resolved photoemission spectroscopy can directly detect the energy and momentum resolved electronic structure of solids, serving as a central role in the discovery and understanding of quantum materials. Here, we report the development of a novel time-resolved ARPES setup equipped with a table-top vacuum ultraviolet laser source with a photon energy of 10.8 eV and a time-of-flight analyzer. The light source is obtained through the generation of ninth harmonics of a 1030 nm Yb fiber-based amplified laser (290 fs, 100 μJ). The photon flux can reach 5 × 1012 photons/s at 333 kHz. We demonstrate its performance in ARPES measurements of the polycrystalline gold film and the electronic structure of the topological insulator Bi2Te3. By introducing a pump beam, we make a pump–probe experiment to detect unoccupied electronic states of Bi2Te3. This setup can achieve an energy resolution of 21.6 meV and a temporal resolution of 296 fs with the tunability of the polarization and repetition rates. This system can provide an important platform to study the non-equilibrium band structure of complex quantum materials with exceptional energy resolution at high repetition rates.
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Hu, Yong, Xianxin Wu, Andreas P. Schnyder et Ming Shi. « Electronic landscape of kagome superconductors AV3Sb5 (A = K, Rb, Cs) from angle-resolved photoemission spectroscopy ». npj Quantum Materials 8, no 1 (10 novembre 2023). http://dx.doi.org/10.1038/s41535-023-00599-y.
Texte intégralRésumé :
AbstractThe recently discovered layered kagome superconductors AV3Sb5 (A = K, Rb, Cs) have garnered significant attention, as they exhibit an intriguing combination of superconductivity, charge density wave (CDW) order, and nontrivial band topology. As such, these kagome systems serve as an exceptional quantum platform for investigating the intricate interplay between electron correlation effects, geometric frustration, and topological electronic structure. A comprehensive understanding of the underlying electronic structure is crucial for unveiling the nature and origin of the CDW order, as well as determining the electron pairing symmetry in the kagome superconductors. In this review, we present a concise survey of the electronic properties of AV3Sb5, with a particular focus on the insights derived from angle-resolved photoemission spectroscopy (ARPES). Through the lens of ARPES, we shed light on the electronic characteristics of the kagome superconductors AV3Sb5, which will pave the way for exciting new research frontiers in kagome-related physics.
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Tseng, Yi, Eugenio Paris, Kai P. Schmidt, Wenliang Zhang, Teguh Citra Asmara, Rabindranath Bag, Vladimir N. Strocov et al. « Momentum-resolved spin-conserving two-triplon bound state and continuum in a cuprate ladder ». Communications Physics 6, no 1 (12 juin 2023). http://dx.doi.org/10.1038/s42005-023-01250-9.
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AbstractStudying multi-particle elementary excitations has provided unique access to understand collective many-body phenomena in correlated electronic materials, paving the way towards constructing microscopic models. In this work, we perform O K-edge resonant inelastic X-ray scattering (RIXS) on the quasi-one-dimensional cuprate $${{{{{{\rm{Sr}}}}}}}_{14}{{{{{{\rm{Cu}}}}}}}_{24}{{{{{{\rm{O}}}}}}}_{41}$$ Sr 14 Cu 24 O 41 with weakly-doped spin ladders. The RIXS signal is dominated by a dispersing sharp mode ~ 270 meV on top of a damped incoherent component ~ 400-500 meV. Comparing with model calculations using the perturbative continuous unitary transformations method, the two components resemble the spin-conserving ΔS = 0 two-triplon bound state and continuum excitations in the spin ladders. Such multi-spin response with long-lived ΔS = 0 excitons is central to several exotic magnetic properties featuring Majorana fermions, yet remains unexplored given the generally weak cross-section with other experimental techniques. By investigating a simple spin-ladder model system, our study provides valuable insight into low-dimensional quantum magnetism.
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Ran, Pengxu, Bing Lin, Caiyun Hong, Baokai Wang, Xiaopeng Xie, Congying Jiang, K. Tanaka et Rui-Hua He. « Observation of novel in-gap states on alkali metal dosed Ti2O3 film ». Journal of Applied Physics 135, no 9 (1 mars 2024). http://dx.doi.org/10.1063/5.0191245.
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Alkali metal dosing has nowadays been extensively used in angle-resolved photoemission spectroscopy (ARPES) for the in situ surface electron doping of materials to provide access to the unoccupied states. This technique also gives rise to nontrivial physical phenomena, such as the appearance of quantum well states and effects due to alkali metal intercalation. Here, we uncovered a previously unobserved type of electronic behavior induced by alkali metal dosing. By employing ARPES to study the evolution of the electronic structure of the Ti2O3 thin film upon rubidium (Rb) dosing, we found that the electron chemical potential of the system remains unchanged throughout the process. Interestingly, a series of electron-like band dispersions first appear with Rb dosing. A further increase in the Rb dosage leads to the eventual disappearance of the electron-like bands and the emergence of a set of hole-like bands. Our finding enriches the phenomenology brought about by alkali metal surface dosing, suggesting a novel functionality of this popular surface doping technique.
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Hunter, A., C. Putzke, I. Gaponenko, A. Tamai, F. Baumberger et P. J. W. Moll. « Controlling crystal cleavage in focused ion beam shaped specimens for surface spectroscopy ». Review of Scientific Instruments 95, no 3 (1 mars 2024). http://dx.doi.org/10.1063/5.0186480.
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Our understanding of quantum materials is commonly based on precise determinations of their electronic spectrum by spectroscopic means, most notably angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy. Both require atomically clean and flat crystal surfaces, which are traditionally prepared by in situ mechanical cleaving in ultrahigh vacuum chambers. We present a new approach that addresses three main issues of the current state-of-the-art methods: (1) Cleaving is a highly stochastic and, thus, inefficient process; (2) fracture processes are governed by the bonds in a bulk crystal, and many materials and surfaces simply do not cleave; and (3) the location of the cleave is random, preventing data collection at specified regions of interest. Our new workflow is based on focused ion beam machining of micro-strain lenses, in which shape (rather than crystalline) anisotropy dictates the plane of cleavage, which can be placed at a specific target layer. As proof-of-principle, we show ARPES results from micro-cleaves of Sr2RuO4 along the ac plane and from two surface orientations of SrTiO3, a notoriously difficult to cleave cubic perovskite.
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Battisti, I., W. O. Tromp, S. Riccò, R. S. Perry, A. P. Mackenzie, A. Tamai, F. Baumberger et M. P. Allan. « Direct comparison of ARPES, STM, and quantum oscillation data for band structure determination in Sr2RhO4 ». npj Quantum Materials 5, no 1 (décembre 2020). http://dx.doi.org/10.1038/s41535-020-00292-4.
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AbstractDiscrepancies in the low-energy quasiparticle dispersion extracted from angle-resolved photoemission, scanning tunneling spectroscopy, and quantum oscillation data are common and have long haunted the field of quantum matter physics. Here, we directly test the consistency of results from these three techniques by comparing data from the correlated metal Sr2RhO4. Using established schemes for the interpretation of the experimental data, we find good agreement for the Fermi surface topography and carrier effective masses. Hence, the apparent absence of such an agreement in other quantum materials, including the cuprates, suggests that the electronic states in these materials are of different, non-Fermi liquid-like nature. Finally, we discuss the potential and challenges in extracting carrier lifetimes from photoemission and quasiparticle interference data.
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Benter, S., M. Bianchi, D. Pan, J. Zhao, H. Q. Xu, R. Timm, Ph Hofmann et A. Mikkelsen. « 2D electron gas formation on InAs wurtzite nanosheet surfaces ». Applied Physics Letters 124, no 15 (8 avril 2024). http://dx.doi.org/10.1063/5.0200217.
Texte intégralRésumé :
The two-dimensional electron gas (2DEG) that forms on a semiconductor surface can be used to explore a variety of phenomena in quantum physics and plays an important role in nanoscale electronics, such as transistors. Controlling its formation is, thus, relevant. Using angle-resolved photoemission spectroscopy (ARPES) and accumulating the signal over many nanocrystals, we find that on clean InAs nanosheets with non-polar surfaces and wurtzite (WZ) crystal structures, a 2DEG can be observed at the Γ-point. We suggest that the step morphology on the WZ InAs specimens facilitates the appearance of the electron gas, since previous studies on InAs nanowire surfaces with the same crystal facet and a similar defect density did not exhibit a 2DEG. Subsequently, bismuth deposition leads to the disappearance of the 2DEG as well as a shift of the valence band. This is in contrast to previous observations on InAs surfaces, in which metal deposition would lead to the formation of a 2DEG. The control of the 2DEG with the addition of Bi atoms is relevant for applications of InAs nanosheets in quantum technologies. This study also illustrates that ARPES accumulated over several 2D materials oriented randomly around their normal axis can provide valuable information on their band structure with a fast turnover and low irradiation.
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Hu, Yong, Congcong Le, Long Chen, Hanbin Deng, Ying Zhou, Nicholas C. Plumb, Milan Radovic et al. « Magnetic coupled electronic landscape in bilayer-distorted titanium-based kagome metals ». Physical Review B 110, no 12 (19 septembre 2024). http://dx.doi.org/10.1103/physrevb.110.l121114.
Texte intégralRésumé :
Quantum materials whose atoms are arranged on a lattice of corner-sharing triangles, i.e., the kagome lattice, have recently emerged as a captivating platform for investigating exotic correlated and topological electronic phenomena. Here, we combine ultralow temperature angle-resolved photoemission spectroscopy (ARPES) with scanning tunneling microscopy and density functional theory calculations to reveal the fascinating electronic structure of the bilayer-distorted kagome material LnTi3Bi4, where stands for Nd and Yb. Distinct from other kagome materials, LnTi3Bi4 exhibits twofold, rather than sixfold, symmetries, stemming from the distorted kagome lattice, which leads to a unique electronic structure. Combining experiment and theory we map out the electronic structure and discover double flat bands as well as multiple Van Hove singularities (VHSs), with one VHS exhibiting higher-order characteristics near the Fermi level. Notably, in the magnetic version NdTi3Bi4, the ultralow base temperature ARPES measurements unveil an unconventional band splitting in the band dispersions which is induced by the ferromagnetic ordering. These findings reveal the potential of bilayer-distorted kagome metals LnTi3Bi4 as a promising platform for exploring novel emergent phases of matter at the intersection of strong correlation and magnetism. Published by the American Physical Society 2024
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Kabir, Firoza, M. Mofazzel Hosen, Xiaxin Ding, Christopher Lane, Gyanendra Dhakal, Yangyang Liu, Klauss Dimitri et al. « Effect of Dilute Magnetism in a Topological Insulator ». Frontiers in Materials 8 (25 novembre 2021). http://dx.doi.org/10.3389/fmats.2021.706658.
Texte intégralRésumé :
Three-dimensional (3D) topological insulator (TI) has emerged as a unique state of quantum matter and generated enormous interests in condensed matter physics. The surfaces of a 3D TI consist of a massless Dirac cone, which is characterized by the Z2 topological invariant. Introduction of magnetism on the surface of a TI is essential to realize the quantum anomalous Hall effect and other novel magneto-electric phenomena. Here, by using a combination of first-principles calculations, magneto-transport and angle-resolved photoemission spectroscopy (ARPES), we study the electronic properties of gadolinium (Gd)-doped Sb2Te3. Our study shows that Gd doped Sb2Te3 is a spin-orbit-induced bulk band-gap material, whose surface is characterized by a single topological surface state. Our results provide a new platform to investigate the interactions between dilute magnetism and topology in magnetic doped topological materials.
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Lee, K. S., J. J. Kim, S. H. Joo, M. S. Park, J. H. Yoo, Genda Gu et Jinho Lee. « Atomic-scale interpretation of the quantum oscillations in cuprate superconductors ». Journal of Physics : Condensed Matter, 10 mars 2023. http://dx.doi.org/10.1088/1361-648x/acc379.
Texte intégralRésumé :
Abstract Cuprate superconductors display unusual features in both k space and real space as the superconductivity is suppressed - a broken Fermi surface, charge density wave (CDW), and pseudogap. Contrarily, recent transport measurements on cuprates under high magnetic fields report quantum oscillations (QO), which imply rather a usual Fermi liquid behavior. To settle the disagreement, we investigated Bi2Sr2CaCu2O8+δ under a magnetic field in an atomic scale. A particle-hole (p-h) asymmetrically dispersing density of states (DOS) modulation was found at the vortices on a slightly underdoped sample, while on a highly underdoped sample, no trace of the vortex was found even at 13 T. However, a similar p-h asymmetric DOS modulation persisted in almost an entire field of view (FOV). From this observation, we infer an alternative explanation of the QO results by providing a unifying picture where the aforementioned seemingly conflicting evidence from ARPES, SI-STM, and magneto-transport measurements can be understood solely in terms of the DOS modulations.
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Deng Xiang-Wen, Wu Li-Yuan, Zhao Rui, Wang Jia-Ou et Zhao Li-Na. « Application and Prospect of Machine Learning in Photoelectron Spectroscopy ». Acta Physica Sinica, 2024, 0. http://dx.doi.org/10.7498/aps.73.20240957.
Texte intégralRésumé :
Photoelectron spectroscopy serves as a prevalent characterization technique within the realm of material science. Specifically, angle-resolved photoelectron spectroscopy (ARPES) provides a direct method for determining the energy-momentum dispersion relationship and Fermi surface structure of electrons within a material system. This makes ARPES a potent tool for the investigation of many-body interactions and correlated quantum materials. The field of photoelectron spectroscopy has seen continuous advancements, with the emergence of technologies such as time-resolved ARPES and nano-ARPES. Concurrently, the evolution of synchrotron radiation devices has led to the generation of an increasing volume of high throughput and high dimension experimental data. This underscores the growing urgency for the development of more efficient and precise data processing methods, as well as the extraction of deeper physical information. In light of these developments, machine learning is poised to play an increasingly significant role across various fields, including but not limited to ARPES. This paper reviews the application of machine learning in photoelectron spectroscopy, which primarily encompasses three aspects:<br>1.Data Denoising: Machine learning can be utilized for denoising photoelectron spectroscopy data. The denoising process via machine learning algorithms can be bifurcated into two methods. Both of the two methods do not need for manual data annotation. The first approach involves the use of noise generation algorithms to simulate experimental noise, thereby obtaining effective low signal-to-noise ratio to high signal-to-noise ratio data pairs. Alternatively, the second approach can be employed to extract noise and clean spectral data, respectively.<br>2.Electronic Structure and Chemical Composition Analysis: Machine learning can be applied for the analysis of electronic structure and chemical composition. (Angle-resolved) photoelectron spectroscopy contains abundant information about material structure. Information such as energy band structure, self-energy, binding energy, and other condensed matter data can be rapidly acquired through machine learning schemes.<br>3.Prediction of Photoelectron Spectroscopy: the electronic structure information obtained by combining first-principles calculation can also predict the photoelectron spectroscopy. The rapid acquisition of photoelectron spectroscopy data through machine learning algorithms also holds significance for material design. Photoelectron spectroscopy holds significant importance in the study of condensed matter physics. In the context of synchrotron radiation development, the construction of an automated data acquisition and analysis system could play a pivotal role in condensed matter physics research. In addition, adding more physical constraints to the machine learning model will improve the interpretability and accuracy of the model. There exists a close relationship between photoelectron spectroscopy and first-principles calculations with respect to electronic structure properties. The integration of these two through machine learning is anticipated to significantly contribute to the study of electronic structure properties. Furthermore, as machine learning algorithms continue to evolve, the application of more advanced machine learning algorithms in photoelectron spectroscopy research is expected. By building automated data acquisition and analysis systems, designing comprehensive workflows based on machine learning and first-principles methods, and integrating new machine learning techniques, it will help accelerate the progress of photoelectron spectroscopy experiments and facilitate the analysis of electronic structure properties and microscopic physical mechanisms, which will advance the frontier research in quantum materials and condensed matter physics.
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Rahn, M. C., K. Kummer, A. Hariki, K. H. Ahn, J. Kuneš, A. Amorese, J. D. Denlinger et al. « Kondo quasiparticle dynamics observed by resonant inelastic x-ray scattering ». Nature Communications 13, no 1 (17 octobre 2022). http://dx.doi.org/10.1038/s41467-022-33468-6.
Texte intégralRésumé :
AbstractEffective models focused on pertinent low-energy degrees of freedom have substantially contributed to our qualitative understanding of quantum materials. An iconic example, the Kondo model, was key to demonstrating that the rich phase diagrams of correlated metals originate from the interplay of localized and itinerant electrons. Modern electronic structure calculations suggest that to achieve quantitative material-specific models, accurate consideration of the crystal field and spin-orbit interactions is imperative. This poses the question of how local high-energy degrees of freedom become incorporated into a collective electronic state. Here, we use resonant inelastic x-ray scattering (RIXS) on CePd3 to clarify the fate of all relevant energy scales. We find that even spin-orbit excited states acquire pronounced momentum-dependence at low temperature—the telltale sign of hybridization with the underlying metallic state. Our results demonstrate how localized electronic degrees of freedom endow correlated metals with new properties, which is critical for a microscopic understanding of superconducting, electronic nematic, and topological states.
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Kadow, Wilhelm, Hui-Ke Jin, Johannes Knolle et Michael Knap. « Single-hole spectra of Kitaev spin liquids : from dynamical Nagaoka ferromagnetism to spin-hole fractionalization ». npj Quantum Materials 9, no 1 (21 mars 2024). http://dx.doi.org/10.1038/s41535-024-00641-7.
Texte intégralRésumé :
AbstractThe dynamical response of a quantum spin liquid upon injecting a hole is a pertinent open question. In experiments, the hole spectral function, measured momentum-resolved in angle-resolved photoemission spectroscopy (ARPES) or locally in scanning tunneling microscopy (STM), can be used to identify spin liquid materials. In this study, we employ tensor network methods to simulate the time evolution of a single hole doped into the Kitaev spin-liquid ground state. Focusing on the gapped spin liquid phase, we reveal two fundamentally different scenarios. For ferromagnetic spin couplings, the spin liquid is highly susceptible to hole doping: a Nagaoka ferromagnet forms dynamically around the doped hole, even at weak coupling. By contrast, in the case of antiferromagnetic spin couplings, the hole spectrum demonstrates an intricate interplay between charge, spin, and flux degrees of freedom, best described by a parton mean-field ansatz of fractionalized holons and spinons. Moreover, we find a good agreement of our numerical results to the analytically solvable case of slow holes. Our results demonstrate that dynamical hole spectral functions provide rich information on the structure of fractionalized quantum spin liquids.