Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L51: Dirac and Weyl Semimetals: Materials and ModelingType II Weyl Semimetals and BeyondFocus Live

Hide Abstracts 
Sponsoring Units: DMP Chair: Joseph Ross, Texas A&M Univ 
Wednesday, March 17, 2021 8:00AM  8:36AM Live 
L51.00001: Topological Chiral Semimetal: Theory and Experiments Invited Speaker: Guoqing Chang We have shown that KramersWeyl fermions are a universal topological electronic property of all nonmagnetic chiral crystals with spinorbit coupling and are guaranteed by structural chirality, lattice translation, and timereversal symmetry. We determined that all pointlike nodal degeneracies in nonmagnetic chiral crystals with relevant spinorbit coupling carry nontrivial Chern numbers. Kramers–Weyl materials can exhibit a monopolelike electron spin texture and topologically nontrivial bulk Fermi surfaces over an unusually large energy window [G. Chang et al. Nature Materials 17, 978985 (2018)]. Among all the materials, we predicted the RhSi family to exhibit the ideal topological band structures, displaying the largest possible momentum separation of compensative chiral fermions, the largest proposed topologically nontrivial energy window, and the longest possible Fermi arcs on its surface [G. Chang et al. PRL 119, 206401 (2017)]. We present the theory of exotic nonlinear optical responses of topological chiral crystals, including quantized photogalvanic effect in RhSi [G. Chang et al. PRL 119, 206401 (2017)] and robust photocurrents from Fermi arc surface states [G. Chang et al. PRL 124, 166404 (2020)]. We also discuss the experimental discovery of the RhSi family as topological chiral crystals [D. S. Sanchez et al. Nature 567, 500505 (2019) & T. A. Cochran et al. arXiv:2004.11365 (2020)] and additional experiments that our discovery has enabled. (This work is in collaboration with D. S. Sanchez, I. Belopolski, T. A. Cochran, B. J. Wieder, F. Schindler, J. Yin, S. S. Zhang, S. Huang, B. Singh, T. Chang, A. Bansil, T. Neupert, S.Y. Xu, H. Lin, and M. Zahid Hasan) 
Wednesday, March 17, 2021 8:36AM  8:48AM Live 
L51.00002: Observation of a T_{d}1T’ structural phase transition at ambient pressure in Weyl semimetal WTe_{2} Yu Tao, John Schneeloch, Adam Aczel, Despina A Louca Layered transition metal dichalcogenides MoTe_{2} and WTe_{2} are suggested to be Weyl semimetals in their orthorhombic T_{d} phase. These materials exist in bulk forms as stacks of strongly inplane bonded layers with weak van der Waals interlayer interaction and their properties often vary with stacking changes. For example, MoTe_{2} exhibits a first order structural phase transition at ∼260K from a lowtemperature orthorhombic T_{d} phase to a hightemperature monoclinic 1T' phase, with an intermediate pseudoorthorhombic T_{d}* phase seen only on warming. In contrast, it is long believed that WTe_{2} has only the T_{d} phase at ambient pressure since the material was first structurally characterized decades ago. We performed elastic neutron scattering measurements at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory (ORNL) on a WTe_{2} single crystal and observed a T_{d}1T’ structural phase transition at ~565K. The transition proceeds without any hysteresis or intermediate phase. The observation of the 1T' phase in WTe_{2} at ambient pressure adds details to the structural behavior of the Mo_{1x}W_{x}Te_{2} family, and gives new insights into reexamination of theories that lack a transition in WTe_{2}. 
Wednesday, March 17, 2021 8:48AM  9:00AM Live 
L51.00003: Role of Mo substitution on the electronic properties of typeII Weyl semimetal W_{1}_{x}Mo_{x}Te_{2} Bishnu Belbase, Bishnu Karki, Gang Bahadur Acharya, Sobhit Singh, Madhav Ghimire Along with the observation of typeII Weyl semimetallic (WSM) phase, multiple novel quantum phenomena such as pressureinduced superconductivity, extremely large magnetoresistance, and various kinds of Hall responses, have been observed in the Td phase of WTe2 and MoTe2. Interestingly, it has been reported that W_{1x}Mo_{x}Te_{2} also hosts typeII WSM phase [1,2]. Therefore, a systematically study of the electronic structure of TdWTe2 as a function of Mo substitution is quintessential to understand the subtle changes occurring in the electronic topology near the Fermi level. In this work, we use densityfunctional theory calculations to investigate the electronic structure of W_{1x}Mo_{x}Te_{2}_{ }(x=0, 0.25, 0.5, 0.75, and 1.0). We find that the total number of Weyl nodes and their location, Fermi arcs, and surface states are very sensitive to the chemical composition. We will discuss the structural stability, the number of Weyl points, Fermi arcs, etc. as x varies. 
Wednesday, March 17, 2021 9:00AM  9:12AM Live 
L51.00004: Electronphonon Interactions in the Weyl semimetal NbIrTe_{4 }Using Raman Spectroscopy Iraj Abbasian Shojaei, Giriraj Jnawali, Seyyedesadaf Pournia, Samuel M Linser, Howard E Jackson, Leigh Smith, Congcong Le, FuChun Zhang, Brenden Ortiz, Stephen D. Wilson Strong anisotropic behavior of Raman modes has been detected in polarized Raman spectroscopy of a ternary compound NbIrTe_{4} nanoflake. 19 Raman modes of A_{1} and A_{2} symmetries were detected and were consistent with DFT calculations. By rotating the sample the Raman spectroscopy probes different directions of the crystal structure. These measurements were implemented so that the polarization direction of the incident and scattered beams are parallel and perpendicular, respectively. Through analysis of this angular dependence one can extract the Raman tensor elements which depend on electronphonon coupling. By exciting at 633 nm and 514 nm, it is possible to observe the sensitivity of the tensor elements to excitation energy for 19 Raman modes. We find that the mode excitation sensitivity depend strongly on their frequency which indicates that some modes couple much more strongly to electronic states than others. 
Wednesday, March 17, 2021 9:12AM  9:24AM Live 
L51.00005: Evolution of phases in (Ba,Sr)Al4 Danila Sokratov, Prathum Saraf, Chris Eckberg, Daniel J Campbell, Jeffrey W Lynn, Peter Zavalij, Johnpierre Paglione Recent results have shown an emergence of CDW order in SrAl4 at 243K, together with a hysteretic structural transition at 87K from a tetragonal to potentially monoclinic structure. The tetragonal structure of BaAl4 with lattice parameters very close to SrAl4 invites a chemical substitution study to track the reported transitions. We have performed electrical resistivity and magnetic susceptibility measurements, along with xray and neutron scattering on the Ba1xSrxAl4 family. All samples have been grown in selfflux and produce large singlecrystals, seemingly limited by crucible size. 
Wednesday, March 17, 2021 9:24AM  9:36AM Live 
L51.00006: Fingerprint of topology in hightemperature quantum oscillations, Part 1/2 Chunyu Guo, Aris Alexandradinata, Carsten Putzke, FengRen Fan, Shengnan Zhang, QuanSheng Wu, Oleg Yazyev, Kent R Shirer, Maja Bachmann, Eric D Bauer, Filip Ronning, Claudia Felser, Yan Sun, Philip Moll A robust methodology to detect DiracWeyl fermions in topological semimetals by transport or thermodynamic measurements remains an open problem. It is often argued that a πphase in quantum oscillations directly corresponds to the nontrivial Berry phase of topological semimetals. However, the oscillation phase is complicated by multiple contributing factors including the orbital magnetic moment, rendering such correspondences ambiguous for a substantial fraction of topological semimetals. Here, we propose to utilize the temperature dependence of the frequency, F(T), rather than the oscillation phase, as a hallmark signature of topology in quantum oscillations. At temperatures that are comparable to the cyclotron energy, F(T) encodes the energyderivative of the cyclotron mass  a quantity that vanishes for conventional Schroedingertype fermions, yet equals the inverse square of the Fermi velocity for DiracWeyl fermions. Cd_{3}As_{2}, Bi_{2}O_{2}Se and LaRhIn_{5} serve as testing grounds confirming our methodology. Our approach requires no abinitio calculation as input, and is able to identify topological Fermi pockets which are small compared to the Brillouinzone volume  both attributes being ideally suited to identify topological heavyfermion materials. 
Wednesday, March 17, 2021 9:36AM  9:48AM Live 
L51.00007: Fingerprint of topology in hightemperature quantum oscillations, Part 2 Chunyu Guo, Aris Alexandradinata, Carsten Putzke, Amelia K Estry, FengRen Fan, Shengnan Zhang, QuanSheng Wu, Oleg Yazyev, Kent R Shirer, Maja Bachmann, Eric D Bauer, Filip Ronning, Chandra Shekhar, Claudia Felser, Yan Sun, Philip Moll A robust methodology to detect DiracWeyl fermions in topological semimetals by transport or thermodynamic measurements remains an open problem. It is often argued that a $\pi$ phase in quantum oscillations directly corresponds to the nontrivial Berry phase of topological semimetals. However, the oscillation phase is complicated by multiple contributing factors including the orbital magnetic moment, rendering such correspondences ambiguous for a substantial fraction of topological semimetals. Here, we propose to utilize the temperature dependence of the frequency, F(T), rather than the oscillation phase, as a hallmark signature of topology in quantum oscillations. At temperatures that are comparable to the cyclotron energy, F(T) encodes the energyderivative of the cyclotron mass  a quantity that vanishes for conventional Schroedingertype fermions, yet equals the inverse square of the Fermi velocity for DiracWeyl fermions. Cd$_3$As$_2$, Bi$_2$O$_2$Se and LaRhIn$_5$ serve as testing grounds confirming our methodology. Our approach requires no abinitio calculation as input, and is able to identify topological Fermi pockets which are small compared to the Brillouinzone volume  both attributes being ideally suited to identify topological heavyfermion materials. 
Wednesday, March 17, 2021 9:48AM  10:00AM Live 
L51.00008: Pressure Induced Creation and Annihilation of Weyl Points in W_{0.5}Mo_{0.5}Te_{2} Bishnu Karki, Bishnu Belbase, Gang Bahadur Acharya, Sobhit Singh, Madhav Ghimire Weyl semimetals (WSM) are an important class of quantum materials in which the lowenergy quasiparticle excitations of electrons mimic the features of massless Weyl fermions. Pair creation/annihilation of Weyl fermions has been a subject of much research interest in recent years. In this work, by means of the densityfunctional theory calculations, we study the role of external pressure and Mo substitution in the widely studied WSM T_{d}WTe_{2}, i.e., W_{0.5}Mo_{0.5}Te_{2}. We find that Weyl nodes slightly shift in the energy space away from the Fermi level as external pressure gradually increases up to 2 GPa. We notice that new pairs of Weyl nodes start appearing through paircreation mechanism in 220 GPa pressure range, yielding as many as 44 Weyl nodes at 20 GPa. Beyond 20 GPa pressure, some pairs of opposite Weyl nodes start annihilating systematically leaving only 16 Weyl points at 35 GPa, which remains invariant until 45 GPa pressure. 
Wednesday, March 17, 2021 10:00AM  10:12AM Live 
L51.00009: Polarized Transient Reflectance of Type II Weyl Semimetals WTe_{2} and NbIrTe_{4} Samuel M Linser, Giriraj Jnawali, Seyyedesadaf Pournia, Iraj Abbasian Shojaei, Howard E Jackson, Leigh Smith, Congcong Le, FuChun Zhang, Brenden Ortiz, Stephen D. Wilson We characterize ultrafast optical anisotropy in typeII Weyl semimetals WTe_{2} and NbIrTe_{4}, using polarized transient reflectance. We study single nanoflakes excited by an ultrafast (140 fs) 800 nm pulse, and monitor the dynamic reflectance of a tunable polarized NIRMIR probe pulse. CW polarized reflectance measurements establish the biaxial symmetry of a flake's optical anisotropy. A halfwave plate sweeps the probe polarization between critical optical axes and records the dynamic response as a function of angle. The intensity and phase of the transient signal sensitively depends on the probe polarization in both materials, whereas characteristic lifetimes show no clear correlation. In WTe_{2,} we observe a rapid ~1.0 ps decay followed by a slow nanosecondscale relaxation. Likewise in NbIrTe_{4}, we observe a fast ~0.6 ps initial decay followed by a slower nanosecond process. We interpret these results in the context of carrier thermalization and lattice cooling in topological semimetals. 
Wednesday, March 17, 2021 10:12AM  10:24AM Live 
L51.00010: Resonant NonLinear Photocurrent in TypeII Weyl Semimetal WP2 Vincent Plisson, Kenneth Burch Weyl semimetals are topological systems that have generated considerable interest due to their transport properties as well as their nonlinear response to light. Due to the topological nature of the Weyl cones, these systems are very sensitive to nonlinear responses such as the shift and injection current response to polarized light. Optical experiments done on various Weyl semimetals have already shown large photocurrent responses, but so far investigation into enhancement of nonlinear responses due to excitations from the Weyl node has been quite limited. These measurements are experimentally difficult due to the low energy requirement to excite about the node, however excitations between Weyl nodes and the Fermi surface may be a way to avoid this challenge. Here we report on midIR photocurrent measurements performed on the typeII Weyl semimetal WP2. Polarization and wavelength dependence of the response shows a room temperature injection current response resonant with the energy of one of the Weyl nodes. 
Wednesday, March 17, 2021 10:24AM  10:36AM Live 
L51.00011: Electronic Correlations in Nodalline Semimetals Yinming Shao, Alexander N. Rudenko, Jin Hu, Zhiyuan Sun, Yanglin Zhu, Seongphill Moon, Andrew Millis, Shengjun Yuan, Alexander I. Lichtenstein, Dmitry Smirnov, Zhiqiang Mao, Mikhail Katsnelson, Dmitri Basov Dirac fermions with highlydispersive linear bands are usually considered weakly correlated, due to relatively large bandwidths (W) compared to Coulomb interactions (U). With the discovery of nodalline semimetals, the notion of Dirac point has been extended to lines and loops in the momentum space [1]. The anisotropy associated with nodalline structure gives rise to greatly reduced kinetic energy along the line. However, experimental evidence for anticipated enhanced correlations in nodalline semimetals is sparse. Here we report on prominent correlation effects in a nodalline semimetal compound ZrSiSe [2] through a combination of optical spectroscopy and densityfunctionaltheory calculations. We observed two fundamental spectroscopic hallmarks of electronic correlations: strong reduction (1/3) of the free carrier Drude weight and of the Fermi velocity compared to predictions of density functional band theory. The renormalization of Fermi velocity can be further controlled with external magnetic field. ZrSiSe therefore offers the rare opportunity to investigate correlationdriven physics in a Dirac system. 
Wednesday, March 17, 2021 10:36AM  10:48AM Live 
L51.00012: NMR investigations of nodalline semimetal ZrSiTe Yefan Tian, Yanglin Zhu, Rui Li, Zhiqiang Mao, Joseph Hansbro Ross In this work, we have applied ^{125}Te nuclear magnetic resonance (NMR) spectroscopy combined with density functional theory (DFT) to characterize the electronic structure of a single crystal sample of ZrSiTe. Both the NMR shift and the spinlattice relaxation rate (1/T_{1}) clearly show minima at 20 K. The observed Tdependence corresponds to the chemical potential crossing an ungapped 2D Dirac nodal line, which corresponds to the symmetryprotected RX nodal line in ZrSiTe. From the orientation dependence we show that diamagnetism of electrons along this nodal line dominates the lowT shifts, and the results indicate very small or zero nodal line energy dispersion. 1/T_{1} is also dominated by these carriers, with the results agreeing with a model for fluctuating local fields due to very high mobility quasi2D Dirac electrons. At higher temperatures, additional extrema reflect the topology of the bands connecting the protected node to the network of nodal loops in ZrSiTe, and these provide direct evidence of temperaturedriven Lifshitz transitions. 
Wednesday, March 17, 2021 10:48AM  11:00AM Live 
L51.00013: Multiple Dirac Nodes and Symmetry Protected Dirac Nodal Lines in Orthorhombic αRhSi Shirin Mozaffari, Niraj Aryal, Rico Schöenemann,, Kuan Wen Chen, Gregory McCandless, Julia Y Chan, Efstratios Manousakis, Luis Balicas Exotic multifold topological excitations have been predicted and were recently observed in transition metal silicides like βRhSi. We report that interesting topological features of RhSi are also observed in its orthorhombic α phase, which displays multiple types of Dirac nodes very close to the Fermi level ε_{F} . We discuss the symmetry analysis, band connectivity along highsymmetry lines using group representations, band structure, the nature of the Dirac points and of a nodal line occurring near ε_{F} which is protected by the crystalline symmetry. The de Haas–van Alphen effect indicates a Fermi surface in agreement with the calculations. We find an elliptically shaped nodal line very close to ε_{F} around and near the S point on the k_{y}k_{z} plane that results from the intersection of two upsidedown Dirac cones. Both Dirac points of the participating Kramers degenerate bands are only 5 meV apart; hence, an accessible magnetic field might induce a crossing between Dirac subbands. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2024 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700