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 Q23: Electronic Structure of Topological Materials (photoemission, etc.)-II |
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Sponsoring Units: DCMP Chair: Madhab Neupane, University of Central Florida Room: Room 215 |
Wednesday, March 8, 2023 3:00PM - 3:12PM |
Q23.00001: Complex electronic structure evolution in a rare-earth based monopnictide* Anup Pradhan Sakhya, Baokai Wang, Firoza Kabir, Cheng-Yi Huang, Md Mofazzel Hosen, Bahadur Singh, Sabin Regmi, Gyanendra Dhakal, Klauss M Dimitri, Milo X Sprague, Robert Smith, Eric D Bauer, Filip Ronning, Arun Bansil, Madhab Neupane In pursuit of intriguing topological phases, the rare-earth monopnictide (REM) family, which has magnetic ground states that exhibit high magnetoresistance, has emerged to be a growing field of research. Here, we study the evolution of the electronic structure of the candidate REM Dirac semimetal NdSb across the magnetic transition by using high-resolution angle-resolved photoemission spectroscopy along with first-principles density functional-theory based modeling. Three arc-like features in the zone corner and a complex band structure resembling an angel's wing have been discovered. It is revealed that the magnetic transition is what causes this drastic reconstruction of the itinerant bands surrounding the zone center: Specifically, in the antiferromagnetic phase, the Nd 5d electron band backfolds at the Γ point and hybridizes with the Sb 5p hole bands. Our study indicates that antiferromagnetism plays an intricate role in the electronic structure of the REM family. |
Wednesday, March 8, 2023 3:12PM - 3:24PM |
Q23.00002: Electronic Structure of a Non-Symmorphic Kondo Lattice System CeAgSb2 Sawani Datta, Khadiza Ali, Rahul Verma, Arumugam Thamizhavel, Bahadur Singh, Kalobaran Maiti Topological Dirac semimetal with non-symmorphic symmetry (NSS) is one of the most recent discoveries in the field of novel topological quantum materials [1]. The uniqueness of this system is the presence of robust (including spin-orbit coupling) Dirac line nodes with NSS protection. CeAgSb2, is a Kondo system, that exhibits a large anisotropic resistivity and a complex magnetic ground state at a lower temperature [2]. Employing angle-resolved photoemission spectroscopy (ARPES), we find that CeAgSb2 possesses several non-trivial crossings near the Fermi level protected by the NSS. The ARPES data collected at different photon-energies suggest a quasi-2-D behavior which is consistent with the transport results. In addition, we observe energy bands of the surface-states in the near-Fermi-level region along with the non-trivial bulk bands that make the electronic structure complex. Our study shows the CeAgSb2-family of materials as a new platform to study the robust non-symmorphic symmetry-protected Dirac semi-metallic systems with high spin-orbit coupling. |
Wednesday, March 8, 2023 3:24PM - 3:36PM |
Q23.00003: Topological surface states in the Kondo insulator YbB12 revealed via planar tunneling spectroscopy Arijit Gupta, Aaron W Weiser, Laura H Greene, Lucas A Pressley, Yi Luo, Chris J Lygouras, Julia Trowbridge, William A Phelan, Collin L Broholm, Tyrel M McQueen, Wan Kyu Park Planar tunnelling spectroscopy of the Kondo insulator (KI) SmB6 suggests that an interaction between surface Dirac fermions and bulk spin excitons results in incompletely protected topological surface states (TSS) [1]. Studying new topological KIs to gain further insight into the true nature of TSS in these compounds is necessary. Band calculations predict that the KI YbB12 hosts TSS protected by crystalline mirror symmetry [2]. Here we present tunneling conductance spectra obtained from the (001) surface of YbB12 single crystals and discuss them in comparison to SmB6 [1]. The linear conductance at low bias provides strong evidence for the existence of surface Dirac fermions and the double-hump structure in the negative bias region is associated with hybridized band edges, in agreement with the theory [2]. Although these similarities with SmB6 are suggestive of the existence of TSS in YbB12 in agreement with other experiments [3], we also discuss the detailed discrepancy attesting that the exact nature of its TSS is different from SmB6. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q23.00004: Tunneling spectroscopic study of the topological Kondo insulator SmB6 via second harmonic measurements Robert M Huber, Mohammad Irfan, Laura H Greene, Wan Kyu Park In tunneling spectroscopy, it is well established that the first harmonic signal can be measured to determine the electronic density of states (DOS) in a material of interest. Naturally, one may wonder if the second harmonic signal has any physical meaning. In the case of strong-coupled Bardeen-Cooper-Schrieffer (BCS) superconductors, the second harmonic signal can be measured to determine the phonon modes involved in Cooper pairing [1]. This is because the BCS DOS is saliently modified due to a large self-energy correction caused by strong coupling. Our previous tunneling studies on the topological Kondo insulator SmB6 have suggested that spin excitons, bosonic bulk excitations, interact with topological surface states to modify their DOS [2,3]. In this talk, we discuss the results of applying second harmonic measurement techniques to SmB6 tunnel junctions. Of particular interest is an antisymmetric peak structure at ± 0.8 mV which persists up to ~5 K, accompanied by two distinct peaks at 4.5 meV and 8.5 meV persisting above 20 K and up to ~12 K, respectively. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q23.00005: Parallel spin-momentum locking in a chiral topological semimetal Jonas A Krieger, Samuel Stolz, Iñigo Robredo, Kaustuv Manna, Emily C McFarlane, Mihir Date, Eduardo B Guedes, J. Hugo Dil, Chandra Shekhar, Qun Yang, Mao Lin, Vladimir N Strocov, Banabir Pal, Matthew D Watson, Timur Kim, Cephise Cacho, Federico Mazzola, Jun Fujii, Ivana Vobornik, Stuart Parkin, Barry Bradlyn, Claudia Felser, Maia Garcia Vergniory, Niels B Schröter We present experimental evidence for parallel spin-momentum locking of a multifold fermion in the chiral topological semimetal PtGa. While orthogonal spin-momentum locking, such as Rashba spin-orbit coupling has been studied for decades and inspired a vast number of applications, its natural counterpart, the purely parallel spin-momentum locking over a full Fermi surface, has so far remained elusive in experiments. Recently, chiral topological semimetals that host single- and multifold band crossings have been predicted to realize such parallel locking [1-4]. We use spin- and angle-resolved photoelectron spectroscopy to probe the spin-texture of the topological Fermi-arc surface states in PtGa and find that the spin points orthogonal to the Fermi surface contour for momenta close to the projection of the bulk multifold fermion, which is consistent with parallel spin-momentum locking of the latter [5]. |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q23.00006: Observation of Weyl fermion states in 2D ferromagnetic electride Gd2C via angle-resolved photoemission spectroscopy Chan-young Lim, Sunghun Kim, Yeonghoon Lee, Jaehun Cha, Gyubin Lee, Dinesh Thapa, Jonathan D Denlinger, Seong-Gon Kim, Sung Wng Kim, Yeongkwan Kim Electrides are materials with interstitial anionic electrons (IAEs) decoupled from atomic orbitals and localized in potential cages formed by cationic atoms. The decoupling provides the possibility of pure electron state which is manifested as interesting properties, such as low work function and weak electron – phonon interaction. Recently, the formation of topological states with IAEs are expected for certain electride materials. 2D electride Gd2C is one of the candidates of topological electrides, where Weyl semimetalic states are predicted due to ferromagnetism that breaks the time-reversal symmetry. However, such topological electronic structure of Gd2C has not been investigated experimentally. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q23.00007: Direct observation of Dirac nodal-line fermions in a mixed-anion superconductor HfP2-xSex Yukimi Nishioka, Satoshi Ishizaka, Kenta Kuroda, Akihiro Ino, Shiv Kumar, Kenya Shimada, 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 In recent years, there has been an active exploration of materials for superconductors with Dirac nodal-line in their electronic structure. MSiCh (M=Zr, Hf; Ch=S,Se) is known as an ideal Dirac nodal-line semimetal with a Si square-net as a glide plane. It is then expected that the crystal structure of MSiCh can give us a hint for material exploration of nodal-line superconductors. Here we focus on a superconductor MP2-xChx, which is isostructural to MSiCh with a P-square net. Previously, we predicted and observed the nodal-line accompanied by fast Dirac particles in ZrP1.24Se0.57. In order to systematically understand the changes in electronic structure by different elements, we have performed an angle-resolved photoelectron spectroscopy of HfP1.48Se0.37 using synchrotron radiation. We have found the nodal-loop with the fastest Dirac velocity (1.3×106 m/s). Its origin and the effect of spin-orbit coupling will be discussed by comparing with the results of MSiS and ZrP1.24Se0.57 in terms of lattice constants and the energy of the elemental orbitals. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q23.00008: Observation of gapless nodal-line states in NdSbTe Sabin Regmi, Robert Smith, Anup Pradhan Sakhya, Milo X Sprague, Mazharul Islam Mondal, Iftakhar Bin Elius, Nathan Valadez, Andrzej Ptok, Dariusz Kaczorowski, Madhab Neupane The recent research interest in ZrSiS-type lanthanide (Ln)-based LnSbTe family of materials comes from the possibility of intermixing of electronic correlations and magnetic ordering of the Ln 4f electrons with topological states including nodal-line and non-symmorphic Dirac states that the ZrSiS family is famous for. In this work, we carried out a study on one such material – NdSbTe – by using angle-resolved photoemission spectroscopy supported by first-principles calculations and thermodynamic measurements. We present experimental detection of multiple gapless nodal lines within -1 eV binding energy, two of them residing along the X-R direction and one formed by polarization-sensitive steep bands lying across the G-M direction. This work unveils the previously unexplored topological electronic structure in NdSbTe providing another distinct platform to understand the Ln-dependent electronic properties in the LnSbTe family of materials. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q23.00009: Evolution of structural, magnetic and charge order in AAl4 series (A=Ba,Sr,Eu) Danila Sokratov BaAl4 and its derived crystal structures host a variety of complex phenomena, including high-temperature superconductivity, charge and spin-density waves, and various topological phases. The SrAl4 and EuAl4 compounds have been reported to show CDW order at 243K and 140K respectively, however the BaAl4 compound contains no such order. Here, we report chemical substitution studies of the Ba1-xEuxAl4 and Ba1-xSrxAl4 compounds containing electrical resistivity, magnetic susceptibility, and x-ray measurements. CDW order spontaneously appears at critical Eu and Sr substitution near x = 0.7, after which it slowly increases to its maximum at x = 1. We present a study of structural and charge order in these series. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q23.00010: Hidden symmetries, Dirac fermions, and topological phase transitions in graphene nanoribbons Nikita V Tepliakov, Johannes Lischner, Efthimios Kaxiras, Arash A Mostofi, Michele Pizzochero We present a theory of the semiconducting state in armchair graphene nanoribbons (AGNRs), a promising class of materials for post-silicon logic electronics. We focus on a specific class of AGNRs of width n=3p+2, where n is the number of carbon atoms across the nanoribbon and p is an integer. Using tight-binding model Hamiltonians and first-principles calculations, we show that the energy gap in such AGNRs originates from the breaking of a previously overlooked hidden symmetry by long-range hopping interactions and structural distortions at the nanoribbon edges. This hidden symmetry can be manipulated through the application of in-plane lattice strain, which can be used to fine tune the energy gap. We further show that lattice strain exceeding a critical value leads to the emergence of Dirac points at the Fermi level and a topological phase transition. Our findings thus establish a novel interpretation of the semiconducting nature of this class of graphene nanoribbons and open new avenues for engineering their topological quantum phases. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q23.00011: Intrinsic in-Plane Anomalous Hall Effect Hui Wang, Yue-Xin Huang, Cong Xiao, Shengyuan A Yang The recent experimental finding of in-plane anomalous Hall effect (IPAHE) opens avenues for exploring the intriguing interplay of in-plane magnetic field and anomalous Hall physics. However, the existing framework relies exclusively on a spin origin, and does not uncover the responsible band geometric properties intrinsic to materials. We reveal that two new intrinsic band geometric quantities-anomalous orbital polarizability (AOP) and anomalous spin polarizability (ASP)-can give rise to an intrinsic bilinear IPAHE. The ASP is allowed in spin-orbit coupled band structures. The AOP originates from the minimal coupling and does not require spin-orbit coupling (SOC). Combined with first-principles calculations, we demonstrate the first quantitative evaluation of the IPAHE in topological semimetals TaSb2, NbAs2 and SrAs3. While the orbital and spin contributions are comparable in TaSb2, the orbital mechanism is completely dominant in NbAs2 and SrAs3 with weaker SOC. In particular, the AOP contribution by the gapped topological nodal-loop across the Fermi surface in SrAs3 is responsible for the effect, rendering a good platform for exploring the manifestation of momentum space topological structures in exotic transport phenomena. |
Wednesday, March 8, 2023 5:12PM - 5:24PM |
Q23.00012: Kramers nodal lines and Weyl fermions in SmAlSi Yichen Zhang, Yuxiang Gao, Xuejian Gao, Shiming Lei, Zhuoliang Ni, Ji Seop Oh, Jianwei Huang, Sergey Gorovikov, Makoto Hashimoto, Donghui Lu, Jonanthan Denlinger, Robert J Birgeneau, Liang Wu, Kam Tuen Law, Emilia Morosan, Ming Yi Kramers nodal lines (KNLs) have recently been proposed theoretically as a special type of Weyl line degeneracy that connects time reversal invariant momenta, are robust to spin orbit coupling (SOC), and are inherent to all non-centrosymmetric achiral crystal structures. Through lattice symmetry breaking, they can be regarded as the parent phase of Kramers Weyl semimetals via topological phase tuning, leading to unusual spin, magneto-electric, and optical properties. Here we identify experimentally the existence of novel KNLs in SmAlSi, a non-centrosymmetric metal that develops incommensurate spin density wave order at low temperatures. Using angle-resolved photoemission spectroscopy, density functional theory calculations, and magneto-transport methods, we provide evidence for the symmetry-protected KNLs, as well as Weyl fermions under the broken inversion symmetry in the paramagnetic phase of SmAlSi. We discuss the nesting possibilities regarding the emergent magnetic orders in SmAlSi. More generally, we establish SmAlSi and the large family of isostructural analogs as a rich material platform for tuning topological phases and exploring correlated topology. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q23.00013: Realization of Practical Eightfold Fermions and Fourfold van Hove Singularity in TaCo2Te2 Hongtao Rong Space groups describing the symmetry of lattice structure allow the emergence of fermionic quasiparticles with various degeneracy in the band structure. Theoretical efforts have predicted many materials hosting fermions with the highest degeneracy, i.e., eightfold fermions, yet lacking experimental realization. Here, we explore the band degeneracies in TaCo2Te2 crystals. Through systematic experimental and theoretical analyses, we establish TaCo2Te2 as a nonsymmorphic crystal with negligible spin-orbit coupling (SOC) and long range magnetic order. These critical properties guarantee the first realization of practical eightfold fermions and fourfold van Hove singularity, as directly observed by photoemission spectroscopy. TaCo2Te2 serves as a topological quantum critical platform, which can be tuned into various magnetic, topologically trivial and nontrivial phases by adding strain, magnetic field or SOC. The latter is demonstrated by our first principle calculation, which shows that enhancing SOC in TaCo2Te2 will promote the experimental observation of bulk hourglass fermions. Our results establish TaCo2Te2 as a unique platform to explore states of matter intertwining magnetism, correlation, symmetry, and band topology. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q23.00014: Visualization of optical polarization transfer to photoelectron spin vector emitted from a spin-orbit coupled surface state Kenta Kuroda, Koichiro Yaij, Ryo Noguchi, Ayumi Harasawa, Shik Shin, Takeshi Kondo, Fumio Komori Similar to light polarization that is selected by a superposition of the optical basis, the electron spin direction can be controlled through a superposition of the spin basis. We investigate such a spin interference occurring in the photoemission of a spin-orbit coupled surface state in Bi2Se3 by using spin- and angle-resolved photoemission spectroscopy combined with a laser light source (laser-SARPES). Our laser-SARPES with three-dimensional spin detection and tunable laser polarization including elliptical and circular polarization enables us to directly visualize how the direction of the fully polarized photoelectron spin changes according to the optical phase and orientation of the incident laser polarization. By this advantage of our laser-SARPES, we demonstrate that such optical information can be projected to the three-dimensional spin vector of the photoelectrons. Our results, therefore, present a spin-polarized electron source permitting us to optically control the pure spin state pointing to an arbitrary direction. |
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