Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session S23: Electronic structure of topological materials (photoemission, etc.)-III |
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Sponsoring Units: DCMP Chair: Muhammad Shattique, University of California, Merced Room: Room 215 |
Thursday, March 9, 2023 8:00AM - 8:12AM |
S23.00001: Geometry-induced spin-filtering in photoemission maps from WTe2 surface states Lukasz Plucinski, Tristan Heider, Gustav Bihlmayer, Jakub Schusser, Friedrich Reinert, Ján Minár, Stefan Blügel, Claus M Schneider We demonstrate that an important quantum material WTe2 exhibits a new type of geometry-induced spin-filtering effect in photoemission, stemming from low symmetry that is responsible for its exotic transport properties [1]. Through the laser-driven spin-polarized angle-resolved photoemission Fermi surface mapping, we showcase highly asymmetric spin textures of electrons photoemitted from the surface states of WTe2. Such asymmetries are not present in the initial state spin textures, which are bound by the time-reversal and crystal lattice mirror plane symmetries. The findings are reproduced qualitatively by theoretical modeling within the one-step model photoemission formalism. The effect could be understood within the free-electron final state model as an interference due to emission from different atomic sites. The observed effect is a manifestation of time-reversal symmetry breaking of the initial state in the photoemission process, and as such it cannot be eliminated, but only its magnitude influenced, by special experimental geometries. |
Thursday, March 9, 2023 8:12AM - 8:24AM |
S23.00002: Exploring the potential of Na3Bi thin films as high-brightness photocathodes Vivek Anil, Christopher T Parzyck, Elena Echeverria, Alice Galdi, Chad A Pennington, Jared Maxson, Kyle M Shen Photocathodes are integral components of a wide variety of x-ray and electron beam based tools, and the spatio-temporal resolution of these instruments is often limited by the intrinsic brightness of the electron beam when it is emitted from the source material. For photocathodes derived from epitaxial thin films, the band structure and surface termination can be engineered to enhance beam brightness for next generation electron sources. In this talk, we explore topological materials, particularly Dirac semimetals, as potential low mean transverse energy photocathodes. We discuss the synthesis of thin film Na3Bi by molecular beam epitaxy. From our angle-resolved photoemission spectroscopy measurements, we extract the mean transverse energy and work function of our Na3Bi films and compare our results to theoretical expectations. |
Thursday, March 9, 2023 8:24AM - 8:36AM |
S23.00003: Emergence of topological and trivial interface states in VSe2 films coupled to Bi2Se3 Joseph A Hlevyack, Yang-Hao Chan, Meng-Kai Lin, Tao He, Wei-Hsiang Peng, Ellen Royal, Mei-Yin Chou, Tai-Chang Chiang Engineering fault-tolerant topological devices inevitably requires coupling topological materials with ordinary metal contacts, which can impact the functionality of a nanoscale device architecture used for manipulating spin information. While interfacing ordinary metals with the prototypical topological insulator Bi2Se3 could foster the long-range propagation of spin-polarized states, we report instead the emergence of both topological and trivial Rashba-type interface states in trivial metal VSe2 films grown on Bi2Se3, all predominantly localized near the VSe2/Bi2Se3 interface. Their strongly decaying spectral weights are unveiled through thickness-dependent angle-resolved photoemission, which are then well-reproduced by our first-principles model for the mixed system’s spectral function. Our findings not only underscore potential design constraints of spin-polarized states in real topological devices but also uncover further the possible hybridization interactions between trivial and nontrivial materials, while offering a new, unique approach for examining localized symmetry-protected states in hybrid structures. |
Thursday, March 9, 2023 8:36AM - 8:48AM |
S23.00004: Anion mixing effects on the electronic structure of a phosphorus-based Dirac nodal-line superconductor ZrP2-xSex Akihiro Ino, Satoshi Ishizaka, Takuya Kubo, Takashi Kono, Yudai Miyai, Hitoshi Takita, Wumiti Mansuer, Shiv Kumar, Kenya Shimada, Shigenori Ueda, Hijiri Kito, Izumi Hase, Shigeyuki Ishida, Kunihiko Oka, Hiroshi Fujihisa, Yoshito Gotoh, Yoshiyuki Yoshida, Akira Iyo, Hiraku Ogino, Hiroshi Eisaki, Kenji Kawashima, Yousuke Yanagi, Akio Kimura Recently, a large family of superconductors emerged as mixed-anion layered phosphides, AP2-xXx (A = Zr, Hf; X = Se, S), which is based on nonsymmorphic phosphorus square-net lattice. |
Thursday, March 9, 2023 8:48AM - 9:00AM Author not Attending |
S23.00005: Ultrafast Dynamics of Laser-Excited Topological Edge States in Graphene Nanoribbon Heterostructures Jan-Philip Joost, Michael Bonitz The electromagnetic properties of finite graphene nanoribbon (GNR) heterostructures are strongly affected by localized topological edge states [1]. Recently, we showed for 7-9-armchair-GNRs that the increased electronic correlations of these states results in increased magnetic moments at the ribbon edges accompanied by a significant energy renormalization of the topological end states, even in the presence of a metallic substrate [2]. Here, we improve the description of the system by including long-range Coulomb interactions within the Pariser–Parr–Pople Model. Employing our newly developed DSL* approximation within the G1–G2 scheme [3-5] we study the ultrafast electron response in a freestanding unit cell of the 7-9-armchair-GNR following a laser excitation. We find that the excited localized edge states play a major role in the subsequent electron dynamics. |
Thursday, March 9, 2023 9:00AM - 9:12AM |
S23.00006: Finite Wavevector Electromagnetic Response in a Weyl Semimetal Model Robert C McKay, Pranav Rao, Barry Bradlyn Recent works have shown that linear and nonlinear optical conductivities of periodic crystals can encode topological and geometric attributes of the electronic bands. To date, work to extend these approaches to calculate responses to spatially inhomogeneous electric and magnetic fields has been limited to expansions around zero wavevector. Here we formulate a theory of linear and nonlinear conductivity for periodic systems at general wavevector. Crucially, our method does not make any assumptions on the form of the underlying Hamiltonian and ensures that current is conserved to all orders in the wavevector. To illustrate our approach, we apply this method to investigate the wavevector-dependent conductivity for a Weyl semimetal model. We examine the Hall response generated from this model, focusing on how the wavevector impacts the expression of topological properties in this response. |
Thursday, March 9, 2023 9:12AM - 9:24AM |
S23.00007: Photo-induced phase transition from topological to trivial insulator in a doped (Pb, Sn)Se Masataka Mogi, Dongsung Choi, Baiqing Lyu, Doron Azoury, Yifan Su, Nuh Gedik The surface electronic structure of a topological crystalline insulator (TCI) is protected by crystal symmetries and can be tuned by various parameters including electric field, pressure, strain, and doping. Here, we use light to control the electronic structure of Bi-doped (Pb, Sn)Se(111) thin film grown by molecular beam epitaxy. In this system, the TCI phase turns into a Z2 topological insulator phase due to lattice distortion. Using time and angle-resolved photoemission spectroscopy, we observe a photo-induced spectral weight suppression at low energies, indicating a topological-insulator to trivial-insulator phase transition. By contrast, such a gap-opening behavior is indiscernible in an undoped (Pb, Sn)Se, which rules out a simple sample heating origin. To explain our results, we propose that local laser irradiation enhancesthe lattice distortion, originally induced by Bi doping, via an anisotropic lattice expansion, which evolves the phase transition from a TCI phase to a trivial insulator phase. Our work may provide a new route to control topological properties by light. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S23.00008: Band structure of ferromagnetic Fe4N thin-film revealed by spin- and angle- resolved photoelectron spectroscopy Karen Nakanishi, Kiyotaka Ohwada, Kenta Kuroda, Kazuki Sumida, Hitoshi Sato, Koji Miyamoto, Taichi Okuda, Shinji Isogami, Keisuke Masuda, Yuya Sakuraba, Akio Kimura Recently, transition metal binary and ternary compounds such as Fe3Ga and Co2MnGa have attracted new attention due to the giant anomalous Hall and Nernst effects caused by Berry curvature in their topological band structures. It has provoked a search for new materials that exhibits the great anomalous conductivity. Fe4N is a well-known ferromagnet with an anti-perovskite structure, showing the inverse tunneling magnetoresistance and anisotropic magnetoresistance. Recently, the large anomalous Nernst coefficient has been reported. To access its origin, we have performed a spin- and angle-resolved photoelectron spectroscopy using synchrotron radiation for a thin-film of Fe4N epitaxially grown on the MgO substrate. We have found electron pockets centered at Γ point as well as M point that are all assigned to be of minority spin. By comparing the experimental result with the first-principles calculation, the electron pockets near Γ and M points are mainly composed of Fe 3d t2g and eg orbitals, respectively, which may assist to understand the anomalous conductivities of Fe4N. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S23.00009: Studies of doping-driven structural phase transitions in (Mo,W)Te2 using ARPES and XPS Matthew C Staab, Robert Prater, Sudheer Anand Sreedhar, Antonio Rossi, Hanshang Jin, Yunshu Shi, Giacomo R Resta, Sergey Y Savrasov, Valentin Taufour, Inna M Vishik (Mo,W)Te2 may be a type-II Weyl semimetal when it is in a structural phase that breaks inversion symmetry. Previously, it has been shown that small amounts of surface electron doping in WTe2 results in changes to surface electronic band structure that are consistent with a metastable shear displacement that locally restores inversion symmetry[1]. Here, we report progress on ARPES and XPS studies of the details of this phenomenon, including using higher temperatures to access states above the Fermi level, XPS to quantify the nature of the chemical changes, and composition-dependence to establish the ubiquity of this phenomenon in the (Mo,W)Te2 series. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S23.00010: In-situ control of topological phase transitions in Cd3As2 detected via the circular photogalvanic effect Bob M Wang, Dong Yu, Henry C Travaglini, Yuqing Zhu, Sergey Y Savrasov Topological devices have garnered intense interest over the previous decades, attributed to their suppressed backscattering, versatile spin texture, strong spin-orbit coupling, chemical robustness, and symmetry protected states. Dirac semimetal Cd3As2 is a member of the topological semimetal family and possesses these characteristics on top of an attractively long spin diffusion length. Topological phase transitions can be achieved reversibly through control over breaking certain symmetries, including crystal inversion and time reversal. |
Thursday, March 9, 2023 10:00AM - 10:12AM Author not Attending |
S23.00011: Quantum oscillation and superconductivity study of the layered Weyl semimetal WTe2 under pressure Wenyan Wang, Jianyu Xie, Wei Zhang, Xinyou Liu, King Yau Yip, Yuen Chung Chan, Kwing To Lai, Swee K Goh We investigate the electronic properties of transition metal dichalcogenides WTe2 under pressure. WTe2 starts to superconduct at ~30 kbar. At 35 kbar, Tc is about 0.95 K. To figure out the relationship between the pressure-induced superconductivity and Fermi surface, we conduct Shubnikov–de Haas quantum oscillation measurements. At ambient pressure, four dominant peaks are observed, whose frequencies are 97 T, 134 T, 150 T and 172 T respectively. By applying pressure, these frequencies and the associated effective masses increase, suggesting the expansion of Fermi surfaces accompanied with enhanced electron-electron correlation. Moreover, we observe a high frequency at ~2000 T and extract a relatively large effective mass m* of 1.8 me at 35 kbar. The enhanced correlation under pressure revealed by our quantum oscillation study provides new information on understanding the pressure-induced superconductivity in WTe2. |
Thursday, March 9, 2023 10:12AM - 10:24AM |
S23.00012: Development of the laser based μ-SARPES machine at HiSOR Takuma Iwata, Kousa Towa, Yukimi Nishioka, Ohwada Kiyotaka, Hideaki Iwasawa, Masashi Arita, Akio Kimura, Kenta Kuroda, Koji Miyamoto, Taichi Okuda Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool to directory observe the electronic structure of solids. In recent years, micro-ARPES [1], which is combined with a micro spot light source, has attracted much attention, since it is found to be very useful to explore the electronic states in topological materials [2], phase-separated correlated systems [3] and transcription samples [4]. |
Thursday, March 9, 2023 10:24AM - 10:36AM |
S23.00013: Deflector mode development for Spin-resolved ARPES Xue Han, Jason Qu, Costel R Rotundu, Zahid Hussain, Zhixun Shen, Jonathan A Sobota Spin-ARPES offers spin resolution in addition to band structure information, which is not accessible by conventional ARPES, hence providing an orthogonal degree of freedom for exploring nontrivial topology, magnetism, and strong correlations in materials. Spin-ARPES faces severe experimental challenges compared to conventional ARPES, such as lower efficiency and difficulties achieving comparable angle/energy resolutions. Therefore, it is crucial to push for instrumentation development to improve the overall performance of the spin-ARPES technique. |
Thursday, March 9, 2023 10:36AM - 10:48AM |
S23.00014: Room temperature excitons in the atomically thin topological insulator Bi:SiC Armando Consiglio, Marcin Syperek, Raul Stühler, Pawel Holewa, Pawel Wyborski, Lukasz Dusanowski, Felix Reis, Sven Höfling, Ronny Thomale, Werner R Hanke, Ralph Claessen, Domenico Di Sante, Christian Schneider The research on topological states of matter saw a remarkable increase in interest since the prediction in graphene of the quantum spin Hall (QSH) effect. Another boost came from the verification, in 2007, of this state of matter. Interesting applications are then made possible by combining symmetry-protected helical edge states and a vanishing bulk conductivity. However, to date, the use quantum Hall materials is limited to very low temperatures because of small band gaps. A progress in this direction is made possible by bismuthene (honeycomb layer of bismuth atoms) grown on a silicon carbide substrate. This material exhibits indeed a direct gap of 1.3 eV at the K-point, proposing itself as an excellent quantum spin Hall insulator for studying excitons in the visible range. In this presentation will be discussed the theoretical results, obtained via many-body perturbation theory and Bethe-Salpeter equation, on the optical resonances in Bi:SiC. By comparing these data with experimental spectroscopic and pump-probe ARPES ones, it will shown that the strong electron-hole interaction have indeed a relevant effect on the optical excitations in Bi:SiC. The results provide the first evidence of excitons in a 2D QSH insulator at room temperature. |
Thursday, March 9, 2023 10:48AM - 11:00AM |
S23.00015: Efficient hydrogen evolution reaction due to topological polarization Ming-Chun Jiang, Guang-Yu Guo, Motoaki Hirayama, Tonghua Yu, Takuya Nomoto, Ryotaro Arita One important application of topological materials is toward surface catalysis, particularly hydrogen evolution reaction (HER), which is an iconic procedure in the field of renewable energy. Based on systematic first-principles calculations for A3B (A = Ni, Pd, Pt; B = Si, Ge, Sn), we propose that topological electric polarization characterized by the Zak phase can be crucial to designing efficient catalysts for the HER. For A3B, we, for the first time in semimetals, show that the Zak phase takes a nontrivial value of π in the whole (111) projected Brillouin zone (PBZ), which causes quantized electric polarization charge accumulation at the surface. While the Zak phase covers the whole PBZ, we believe that the impact of topological properties is more significant than well-studied Weyl semimetals. |
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