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 M25: Dirac and Weyl Semimetals: Theory 1 |
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Sponsoring Units: DCMP Chair: Jen Dailey Lambert Room: Room 217/218 |
Wednesday, March 8, 2023 8:00AM - 8:12AM |
M25.00001: Amorphous chiral semimetals Selma Franca, Adolfo G Grushin Chiral semimetals are known to host multifold fermions, low energy quasiparticles emerging from a generalized Weyl equation with a higher spin [1]. While conventional Weyl fermions result from breaking time-reversal or inversion symmetry, these multifold fermions require crystlline symmetries for their topological protection. Using tight-binding approach, we study the effect of structural disorder on the topological phase in an amorphous CoSi system. |
Wednesday, March 8, 2023 8:12AM - 8:24AM |
M25.00002: Fingerprints of multifold fermions in optics: linear and nonlinear optical responses of CoSi and RhSi Miguel Ángel Sánchez Martínez, Bing Xu, Zhenyao Fang, Zhuoliang Ni, Baozhu Lu, Jörn W Venderbos, Fernando de Juan, Eugene J Mele, Andrew M Rappe, Liang Wu, Darius H Torchinsky, Adolfo G Grushin The 230 space groups, of which only 65 are chiral, describe all possible combinations of non-magnetic crystal symmetries in nature. Materials described by some of these groups host band degeneracies near the Fermi level protected by the corresponding crystal symmetries. A remarkable example of materials exhibiting this type of degeneracies are the topological semimetals RhSi and CoSi. The low-energy quasiparticles emerging near the protected band degeneracies, referred to as multifold fermions, have no counterpart as elementary fermionic particles. We present in this talk the linear optical conductivity of all chiral multifold fermions[1] and show that it provides an experimental fingerprint for each type of multifold fermion. We use a tight-binding model for space group 198, where RhSi and CoSi crystallize, revealing that the location of the chemical potential is crucial to understand the optical response seen in experiments[2,3], determined at low energies by the threefold fermion at the Γ point in both materials, and providing signatures of the existence of a spin-3/2 fourfold fermion in CoSi. Finally, we study the second-harmonic generation of RhSi. We analyze the experimental results using a second-order k·p Hamiltonian and compare our results with density functional theory calculations to provide a comprehensive description of the origin of the different features in the second-harmonic response and their relation to the topological character of the bands in RhSi. |
Wednesday, March 8, 2023 8:24AM - 8:36AM |
M25.00003: Layer number dependence of topological properties in atomically thin films of a ferromagnetic Weyl semimetal Co-based shandite Kazuki Nakazawa, Yasuyuki Kato, Yukitoshi Motome The kagome ferromagnet Co3Sn2S2 exhibits a giant anomalous Hall effect associated with the Weyl nodes in the band structure [1]. Recently, the quantized anomalous Hall effect in the monolayer was predicted theoretically [2], which awaits experimental realization. However, further investigation is required to clarify the role of lattice structure and magnetism, which are often relevant to the band topology in thin films. In this study, we perform the ab initio calculations for Co-based shandite with one, two, and three Co-kagome-layer films of Sn- and S-end surfaces, with special attention to the optimization of stable lattice structures and magnetic states. We find that, in all the Sn-end films, the ferromagnetic state is stabilized and the gapped Weyl nodes evolve systematically with increasing the number of Co layers, which generates a large anomalous Hall effect. In contrast, the S-end cases show different magnetic states depending on the layer number, which leads to different band topology and transport properties. These results provide a hint for the experimental investigation of the Weyl physics in the thin films of Co-based shandite. |
Wednesday, March 8, 2023 8:36AM - 8:48AM |
M25.00004: Chirality-driven topological orbital texture in the chiral multifold semimetal PdGa Qun Yang, Iñigo Robredo, Maia G Vergniory, Binghai Yan, Claudia Felser As a unique crystalline symmetry, chirality displays its significance in topological materials. It nurtures many exotic electronic properties, such as multifold chiral fermions which manifest nontrivial topological charge and spin textures. However, among chiral topological semimetals (TSMs), the essential understanding of the electronic orbital information, i.e. orbital angular momentum (OAM), is rather limited. In this work, a new perspective to comprehend the correlation between OAM and enantiomer recognition in chiral TSMs is presented. We reveal that the OAM of the bulk electronic structure is finite and locked to the electronic momentum, resulting in sign reversal for the opposite enantiomers. Consequently, OAM can be regarded as an intrinsic decisive for enantiomer recognition. In addition, chiral multifold fermions with opposite chirality act as sources and sinks of OAM, which is analogous to the Berry curvature. These findings open a different route for enantiomer recognition by physical properties rather than chemical ones, which could allow for unlocking the origins of enantioselective processes. |
Wednesday, March 8, 2023 8:48AM - 9:00AM |
M25.00005: Temperature-dependent Optical Conductivity for a Simple Model of a Nodal-line Semimetal Under Strain SITA KANDEL We report on the temperature dependent optical conductivity for a simple model of a nodal- line semimetal (NLSM). The effect of strain is included through a parameter α which is effective on the distortion of the energy bands within the first Brillouin zone. With a model Hamiltonian and the Kubo formula, we derive semi-analytic results for both transverse and longitudinal optical conductivity including both intra and interband contributions. We compare our results with those for ZrZiS like material having similar band structure which is different than that of 2D or 3D Dirac or Weyl semimetal. |
Wednesday, March 8, 2023 9:00AM - 9:12AM |
M25.00006: Anomalous Landau Levels in Intrinsic Magnetic Topological Insulators Chao Lei, Perry T Mahon, Allan H MacDonald The intrinsic Magnetic Topological Insulator MnBi2Te4 (MBT) family has been extensively studied recently because of the rich physical properties it displayes in both bulk materials and thin films. The Quantum Anomalous Hall (QAH) effect has been observed in MBT thin films with an odd-number of layers in the absence of magnetic field, and quantized Hall conductivities were also reported in MBT thin films in which magnetic moments have aligned by external magnetic fields. In this talk we will discuss the electronic structure of MBT thin films in the presence of magnetic field, using a simplified effective model [1] that captures the magnetic and topological properties of the intrinsic magnetic topological insulators. We will show that in antiferromagnetic MBT thin films anomalous Landau levels play an important role in both Hall conductivity quantization [2] and in the magnetoelectric response [3]. This talk is related to the bulk theory of the magneto-electric response [4] of the same model discussed in a companion presentation by Mahon, Lei, and MacDonald. |
Wednesday, March 8, 2023 9:12AM - 9:24AM |
M25.00007: Controllable anomalous Hall effect in topological Dirac semimetals with ferromagnetic electrodes Koji Kobayashi, Kentaro Nomura The Hall effect is a fundamental transport phenomenon and essential for spintronics devices, such as magnetic sensors and magnetic memories. Now the Hall effect is attracting a renewed interest since a giant anomalous Hall effect is observed in magnetic Weyl semimetals such as Co3Sn2S2. |
Wednesday, March 8, 2023 9:24AM - 9:36AM |
M25.00008: Influence of the Surface States on the Nonlinear Hall Effect in Weyl Semimetals Diego García Ovalle, Armando Pezo, Aurélien Manchon Linear response phenomena have inspired novel applications in nanoelectronics. The most fundamental example is the anomalous Hall effect, where a transverse charge current is generated in presence of an applied electric field. Nevertheless, the Hall effect vanishes in non-magnetic materials. In view of this fact, Sodemann and Fu suggested in 2015 that a second order Hall effect is allowed in systems with time reversal symmetry and non-centrosymmetric structure stemming from the Berry curvature dipole. Several material candidates such as Weyl semimetals have been proposed as ideal platforms to this nonlinear Hall effect because of their highly dispersive energy bands and the presence of Weyl nodes. However, the impact of their surface states on second order Hall transport driven by the Berry curvature dipole is still unclear. |
Wednesday, March 8, 2023 9:36AM - 9:48AM |
M25.00009: Interaction Stability of the Chiral Anomaly in 1+1d Shuyang Wang, Jay D Sau The chiral anomaly is one of the counter-intuitive quantum effects in field theories with chiral symmetry. In many contexts, the chiral anomaly is a consequence of a topological term in the field theory and therefore not renormalized. However, based on some calculations on relativistic models, recent works have proposed that the chiral anomaly could be modified by interactions in Weyl systems. In this paper, we investigate the interaction stability of the chiral anomaly in different one-dimensional condensed matter systems by interactions. We show that in interacting 1DEG at incommensurate fillings, the chiral charge is defined as the total momentum divided by kF, and the anomaly term originated from the non-gauge-invariance of the stress-energy tensor. With this definition, we find the chiral anomaly to be unrenormalized by interactions. The chiral charge in relativistic field theory is defined as being equal to the conventional current. We find that the chiral anomaly with this definition of chiral charge to be renormalized. We argue that this definition of chiral charge is the only meaningful definition if a back-scattering pinning potential is used to open a weak gap at the Fermi surface. In the presence of repulsive interactions, the chiral charge so defined can be associated with a conserved solitonic chiral charge, which is the total number of solitons and anti-solitons. This renormalized chiral anomaly can be measured by applying an electric field larger than the gap induced by pinning potential. |
Wednesday, March 8, 2023 9:48AM - 10:00AM |
M25.00010: Surface states and anomalies in 3D topological semimetals from momentum-spin multipole moments Yoonseok Hwang, Penghao Zhu, Taylor L Hughes Topological semimetals exhibit a variety of anomalous responses determined by the geometry of their gapless nodal points and lines. For example, 3D Weyl semimetals show the anomalous Hall effect whose conductivity is determined by the chirality weighted momentum dipole moment. In this work, we study 3D Weyl semimetals with vanishing anomalous Hall coefficients, but nonzero mixed quadrupole moments of the momentum and spin. Such a system exhibits a 3D analog of the quantum spin Hall effect. On the 2D surface, gapless surface states are characterized by commuting spin-momentum locking terms in contrast to the anti-commuting spin-momentum locking of Dirac cones. These surface states induce anomalous charge and spin currents under external fields. We study the anomaly cancellation between bulk anfd surface by deriving a bulk topological action with electromagnetic and spin gauge fields and show that the response coefficient is proportional to the mixed momentum-spin quadrupole moment. Finally, we discuss the connection between our system and responses to higher-rank tensor field theory. |
Wednesday, March 8, 2023 10:00AM - 10:12AM |
M25.00011: Dynamical chiral magnetic current and instability in Weyl semimetals Tatsuya Amitani In massless fermionic systems such as Weyl semimetals, it is known that electric currents are induced by magnetic fields, which is called the chiral magnetic effect [1]. In this talk, we will present our recent study that analyzes the chiral magnetic effect driven by a dynamical magnetic field in Weyl semimetals [2]. In particular, their electromagnetic linear responses are investigated based on the effective field theory and on the chiral kinetic theory. Furthermore, we incorporate dissipation in the relaxation-time approximation and study collective excitations coupled with Maxwell electromagnetic fields. |
Wednesday, March 8, 2023 10:12AM - 10:24AM |
M25.00012: Nonlinear photoconductivities and quantum geometry of multifold fermions Hsiu-Chuan Hsu, Jhih-Shih You, Guang-Yu Guo The injection and shift conductivities and their relevant geometrical quantities for multifold fermions, including pseudospin-1 and -3/2 excitations, are studied. For pseudospin-1 fermion, or the triple point fermion (TPF), we utilize the minimal symmorphic model which hosts TPFs protected by C4 rotation symmetry and an anticommuting mirror symmetry. The circular injection conductivity shows quantization as a result of the Chern number of the node. The linear shift conductivity of the TPF model is proportional to the pseudo spin-orbit coupling and independent of photon frequency. For the pseudospin-3/2 excitation, we utilize the effective Hamiltonian for the CoSi family. The circular injection conductivity shows two consecutive plateaus as a result of the Chern number carried by each of the occupied bands. The linear shift conductivity is linearly dependent on the photon frequency. The corresponding Christoffel symbols show a significant peak near the node, suggesting the strong geodesic response in the momentum space near the node. |
Wednesday, March 8, 2023 10:24AM - 10:36AM |
M25.00013: Braid protected topological band structures with unpaired exceptional points J Lukas K König, Emil J Bergholtz, Kang Yang, Jan C Budich We explore loopholes in the non-Hermitian Fermion doubling theorem. In particular, we show how this gives rise to non-trivial exceptions in systems with three or more bands, where the topological structure is non-abelian and the winding number description does not provide the full picture. In a simple three-band model, we show the occurrence of a single, unpaired, exceptional point on a Brillouin zone. This third-order degeneracy cannot be gapped by any small perturbation due to the non-trivial boundary braid. It can only split into simpler (second order) constituent degeneracies that need to be moved around topologically non-trivial loops of the Brillouin zone before being able to fully gap out by pairwise annihilation. |
Wednesday, March 8, 2023 10:36AM - 10:48AM |
M25.00014: Electronic and topological properties of non-Hermitian graphene Riccardo Sorbello, Armando Consiglio, Lavi K Upreti, Ronny Thomale In recent years the study of open systems via non-Hermitian Hamiltonians established itself as a fascinating research topic. Indeed new intriguing features arises, like the presence of a complex spectrum, the loss of bulk-boundary correspondence and the possibility of charge accumulation on one edge of the sample (the latter phenomenon called non-Hermitian skin effect), just to name a few examples. |
Wednesday, March 8, 2023 10:48AM - 11:00AM Author not Attending |
M25.00015: A new unconventional thermoelectric transport in type-I Weyl semimetals Alireza Qaiumzadeh, Thorvald Ballestad, Alberto Cortijo, Maria A Vozmediano We analyze the effect of the tilt vector on the transverse thermoelectric coefficient of Weyl semimetals in the conformal limit. We find a non-monotonic behavior of the thermoelectric conductivity as a function of the tilt perpendicular to the magnetic field, and a linear behavior when the tilt is aligned to the magnetic field. An axial Nernst current is also generated in inversion symmetric Weyl materials when the tilt vector has a projection in the direction of the magnetic field. |
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