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 PP01: V: Dirac and Weyl Semimetals |
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Sponsoring Units: DMP Chair: Cheng-Chien Chen, University of Alabama at Birmingham Room: Virtual Room 1 |
Tuesday, March 21, 2023 9:00AM - 9:12AM |
PP01.00001: Generalized Hatano-Nelson Model Julius Gohsrich, Sharareh Sayyad, Flore K Kunst Non-Hermitian systems attract a lot of attention in recent years as effective description of open quantum systems. A prominent example in this context is the Hatano-Nelson model. While historically the model has short-range non-reciprocal hoppings, long-range hopping has not been systematically studied. In this talk, I will present our results on the generalized Hatano-Nelson model. Using analytical techniques, we demonstrate how the underlying physics of the original Hatano-Nelson model is enriched when longer-range hoppings are also included. I will discuss how the crucial elements of the Hatano-Nelson model, namely, the non-Hermitian skin effect and the exceptional points, are modified for the generalized model.
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Tuesday, March 21, 2023 9:12AM - 9:24AM |
PP01.00002: Topological Nodal Line Semimetals with Chiral Symmetry Faruk Abdulla, Ganpathy N Murthy, Ankur Das Topological semimetals occur in two variants, with the bands touching at point nodes (Weyl or Dirac semimetals), or touching at nodal lines in the Brillouin zone. While Weyl/Dirac semimetals can occur with internal symmetries only (such as time-reversal, charge conjugation, and possibly a product of the two, called chiral/sublattice symmetry), nodal line semimetals have been believed to require more symmetry, such as SU(2) spin rotation or crystalline symmetries. Here we show that in the presence of chiral symmetry, additional symmetries are not necessary to have topological nodal line semimetals. Starting from a generic model Hamiltonian possessing only time-reversal, inversion, and chiral symmetries, which belongs to the Altland-Zirnbauer symmetry class CII, we demonstrate how a topological nodal line semimetal can be obtained by breaking either time-reversal, inversion symmetry, or both. The nodal line semimetal has robust topological surface states protected by chiral symmetry. Our findings will be useful for ongoing explorations of topological nodal line semimetals. |
Tuesday, March 21, 2023 9:24AM - 9:36AM |
PP01.00003: Symmetry-enforced nodal chain phonons Jiaojiao Zhu, Shengyuan A Yang Topological phonons in crystalline materials have been attracting great interest. Most cases studied so far are direct generalizations of the topological states from electronic systems. Here, we reveal a class of topological phonons - the symmetry-enforced nodalchain phonons, which manifest the characteristic of phononic systems. We show that in five space groups with D2d little co-group at a non-time-reversal-invariant-momentum point, the phononic nodal chain is guaranteed to exist owing to the vector basis symmetry of phonons, which is a character distinct from electronic and other systems. In other words, this symmetry enforcement feature of the proposed nodal chain is limited to phononic systems. Interestingly, the chains in these five space groups exhibit two different patterns: for tetragonal systems, they are one-dimensional along the fourfold axis; for cubic systems, they form a threedimensional network structure. Based on first-principles calculations, we identify K2O as a realistic material hosting the proposed nodal-chain phonons. We show that the effect of LO-TO splitting helps to expose the nodal-chain phonons in a large frequency window. In addition, the nodal chains may lead to drumhead surface phonon modes on multiple surfaces of a sample. |
Tuesday, March 21, 2023 9:36AM - 9:48AM |
PP01.00004: Ultrafast magnetization dynamics in the magnetic Weyl semimetal Co3Sn2S2 Mengqian Che, Luyi Yang Co3Sn2S2 is a new magnetic Weyl semimetal, in which strong intrinsic anomalous Hall effect and optical nonlinear responses are found. It has attracted significant interest in exploring its topological and magnetic properties. In this talk, we report on ultrafast magnetic dynamics in this material using time-resolved magneto-optics Kerr rotation. We find both coherent magnon oscillations and thermally driven ultrafast demagnetization. The ferromagnetic resonance (FMR) frequency is measured to be hundreds of gigahertz at low temperatures, which is much faster than other traditional FMR frequencies. The demagnetization dynamics depend strongly on the temperature, showing critical slowing down near the Curie temperature. We also extract the anisotropy field value, magnon lifetime and demagnetization time from the measurements. Our experiment sheds new light on the magnetization dynamics in this novel magnetic Weyl semimetal. |
Tuesday, March 21, 2023 9:48AM - 10:00AM |
PP01.00005: Infrared study of ellipsoidal nodal ring semimetal SrAs3 Jiwon Jeon, Eunjip Choi, Jiho Jang, Hongki Min, Jun Sung Kim, Hoil Kim, Ji Hoon Shim, taesu park, soonjae moon, dong wook kim Dirac/Weyl semimetals, a novel class of quantum materials, are characterized by linearly dispersing energy bands from nodal point that obey relativistic Hamiltonians. For nodal point and nodal line Dirac/Weyl semimetals, optical studies showed unique features such as constant/linear optical conductivity σ1IB(ω) ∝ ω(deff-2)/z (deff = effective lattice dimension and z = energy dispersion dimension) . Here we measured polarization-dependent optical reflectivity on SrAs3 single crystals, a nodal-ring semimetal where Ef crosses only non-trivial band without interruption from trivial bands. For E//x, a flat optical absorption occurs up to 130meV, whereas drastically different behavior is observed for E//z. A SOC gap transition appears at 35meV for both polarizations. We perform theoretical calculations of σ1IB(ω) based on low-energy model Hamiltonian and DFT band calculations, and compare them with experimental σ1IB(ω). The Fermi surface structure (nodal ring vs nodal ellipsoid) and band dispersion (linear vs quadratic) of SrAs3 are unveiled from this comparative study. |
Tuesday, March 21, 2023 10:00AM - 10:12AM |
PP01.00006: Electric field Induced Dzyaloshinskii-Moriya Interaction in Ferromagnetic Weyl Semimetals Yuriy Semenov An early stage of non-trivial manifestation of SOI pertains to the issue of a widespread antisymmetric superexchange interaction in form of Dzyaloshinskii-Moriya interaction (DMI) that is an intrinsic property of the material or structure with broken inversion symmetry. From this point of view, it seems promising to search the mechanisms of asymmetrical spin-spin coupling beyond the superexchange interaction. One of such possibilities was shown to be realized in Weyl semimetals (WSM) where indirect spin-spin interaction via Weyl fermions reveals the antisymmetric spin-spin interaction along with conventional Ruderman--Kittel--Kasuya--Yosida (RKKY) interaction. However, the RKKY interaction mediated by the electron scattering between opposite-chirality Weyl nodes does not contribute to DMI. Moreover, the same chirality fermions in inversion-symmetric WSM cannot induce DMI because of compensative effect of different Weyl nodes [1]. In this study we show that chiral anomaly which results in imbalance of Weyl node populations could be a mediator of DMI appearance for remote spin pairs in WSM of high symmetry. In such materials, the non-collinear magnetic B and electric E fields generate DMI with strength proportional to Dzyaloshinskii vector D=d(BE)n, where a unit vector n is directed along the locations r1 and r2 of interacted spin pair, and constant d can be estimated in terms of typical WSM material constants as d ~1.3 10-4 meV cm/ V T for spins separated on several lattice constants. Thus, the moderate electric field 105 V/cm may induce the observable strength D ~1 meV provided B=0.1 T. By order of magnitude this field strength contributes to demagnetizing fields in most ferromagnets that do not need an external source enhancing B. It has also been shown that remote DMI may generate the skyrmions under the locally applied bias in the ferromagnetic slab revealing a different way of WSM spintronic application. |
Tuesday, March 21, 2023 10:12AM - 10:24AM |
PP01.00007: Fermi surface of type-II Dirac semimetal candidates (Ni, Zr)Te2 investigated using torque magnetometry and density functional theory Thinh Nguyen, Niraj Aryal, David E Graf, Bal K Pokharel, Duncan Miertschin, Dragana Popovic, Keshav Shrestha, Luminita Harnagea We have studied the fermiology of the type-II Dirac semimetal candidates (Ni, Zr) Te2 using torque magnetometry. The measurements were carried out under applied fields up to 35 T and temperatures as low as 0.32 K. Results showed clear de Haas-van Alphen (dHvA) oscillations with one major frequency for ZrTe2 at F ~ 530 T and three major frequencies for NiTe2 at F1 ~ 72 T, F2 ~ 425 T, and F3 ~ 630 T. Berry phase analyses suggested that NiTe2 is a topologically nontrivial system whereas ZrTe2 is a topologically trivial system. Additional analyses using the Lifshitz-Kosevich formula to determine the effective mass of the electron of both NiTe2 and ZrTe2 were also carried out. Electronic band structures were investigated using density functional theory (DFT) to support our experimental data. |
Tuesday, March 21, 2023 10:24AM - 10:36AM |
PP01.00008: Transport signatures of Fermi arcs at twin boundaries in Weyl materials Sahal Kaushik, Nitish Mathur, Iñigo Robredo, Leslie M Schoop, Song Jing, Maia Garcia Vergniory, Jennifer Cano One of the most striking signatures of Weyl fermions is their surface Fermi arcs. Less known is that Fermi arcs can also be localized at internal twin boundaries where two Weyl materials of opposite chirality meet. In this work, we derive constraints on the topology and connectivity of these ``internal Fermi arcs.'' We show that internal Fermi arcs can exhibit transport signatures and propose two probes: quantum oscillations and a quantized chiral magnetic current. We propose merohedrally twinned B20 materials as candidates to host internal Fermi arcs, verified through both model and ab initio calculations. Our theoretical investigation sheds light on the topological features and motivates experimental studies into the intriguing physics of internal Fermi arcs. |
Tuesday, March 21, 2023 10:36AM - 10:48AM |
PP01.00009: The circular photogalvanic effect in disordered Weyl semimetals Ang-Kun Wu, Jedediah H Pixley, Justin H Wilson In a noninteracting chiral Weyl semimetal, the circular photogalvanic effect (CPGE) is quantized with a quantum due to band topology. We theoretically study the fate of this quantization in the presence of quenched short-range disorder. To calculate the non-linear response of the system, we utilize the kernel polynomial method via a triple expansion in terms of Chebyshev polynomials. Results will be presented on the CPGE in disordered Weyl semimetals on large system sizes, where non-perturbative rare region effects and the stability of the quantization are explored. |
Tuesday, March 21, 2023 10:48AM - 11:00AM |
PP01.00010: Tunable unconventional kagome superconductivity in charge ordered RbV3Sb5 and KV3Sb5 Zurab Guguchia, Charles Mielke, Debarchan Das, Ritu Gupta, Jiaxin Yin, Hongxiong Liu, Qiangwei Yin, Morten Holm Christensen, Zhijun Tu, Chunsheng Gong, Nana Shumiya, Tsotne Gamsakhurdashvili, Mathias Elender, Pengcheng Dai, Alex Amato, Youguo Shi, Hechang Lei, Rafael M Fernandes, Zahid M Hasan, Hubertus Luetkens, Rustem Khasanov Unconventional superconductors often feature competing orders, small superfluid density, and nodal electronic pairing. While unusual superconductivity has been proposed in the kagome metals AV3Sb5, key spectroscopic evidence has remained elusive. Here we utilize pressure-tuned (up to 2.25 GPa) and ultra-low temperature (down to 18 mK) muon spin spectroscopy to uncover the unconventional nature of superconductivity in RbV3Sb5 and KV3Sb5. At ambient pressure, we detect a two-step enhancement of the width of the internal magnetic field distribution sensed by the muon ensemble in RbV3Sb5, indicative of time-reversal symmetry breaking charge order below T1' = 110 K with an additional transition at T2' = 50 K. Remarkably, the superconducting state displays a nodal energy gap and a reduced superfluid density, which can be attributed to the competition with the novel charge order. Upon applying pressure, the charge-order transitions are suppressed, the superfluid density increases, and the superconducting state progressively evolves from nodal to nodeless. Once optimal superconductivity is achieved, after either full or partial suppression of charge order, we find a superconducting pairing state that is not only fully gapped, but also spontaneously breaks time-reversal symmetry. Our results point to unprecedented tunable nodal kagome superconductivity competing with time-reversal symmetry-breaking charge order and offer unique insights into the nature of the pairing state. |
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