Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session F04: Dirac/Weyl Semimetals  Transport II (including STM, etc)Focus

Hide Abstracts 
Sponsoring Units: DMP Chair: Hsu Liu, Univ of Cambridge Room: BCEC 107C 
Tuesday, March 5, 2019 11:15AM  11:27AM 
F04.00001: Shubnikovde Haas oscillations of topological metal Pd_{3}Pb Nirmal Ghimire, Mojammel Alam Khan, Antia S. Botana, J Samuel Jiang, John Mitchell The recent realization of topological electronic states such as Dirac and Weyl fermions in real materials and their potential for future energy and electronics applications has motivated interest in the study of new forms of topological behavior embodied through new materials. Pd_{3}Pb is one such candidate predicted recently to host unique topological features, including a dispersionless band near the Fermi level and triple nodal points hosting Dirac fermions and open Fermi arcs. Here, we report the crystal growth and electric transport properties of Pd_{3}Pb. Our low field magnetoresistance measurements indicate an anisotropic Fermi surface. We found that Pd_{3}Pb manifests a large transverse magnetoresistance, which reaches 650% at 1.8 K and 14 T, and pronounced Shubnikovde Haas (SdH) oscillations. Preliminary analysis of the field dependence of the SdH oscillations points to the likelihood of nontrivial Berry phase in Pd_{3}Pb. Further studies in high field limit are desirable to extend the realization of the topological properties of the predicted novel fermions in this material. 
Tuesday, March 5, 2019 11:27AM  11:39AM 
F04.00002: Quantum oscillations in topological semimetal candidate CaSn_{3} K A M Hasan Siddiquee, Riffat Munir, Charuni Dissanayake, Xinzhe Hu, Swapnil Yadav, Yasumasa Takano, Eun Sang Choi, Yasuyuki Nakajima Binary stannide CaSn_{3} with a centrosymmetric cubic structure is theoretically predicted to be a topologically nontrivial semimetal, and undergoes superconductivity at T_{c} ≈ 4.2K, providing an excellent platform for the understanding of interplay between topology and superconductivity. Here, we report a detailed study of de Haas–van Alphen (dHvA) quantum oscillations for CaSn_{3} single crystals via torque magnetometry in high magnetic fields up to 35T. Analyzing the dependence of dHvA oscillation frequency and amplitude on temperatures and field angles, we will review the effective carrier masses and the normal state fermiology, and also discuss the nontrivial Berry phase in CaSn_{3}. 
Tuesday, March 5, 2019 11:39AM  11:51AM 
F04.00003: Vector field STM study on transition metal based kagome magnet Jiaxin Yin, Songtian Sonia Zhang, Guoqing Chang, Zurab Guguchia, Shuang Jia, Hechang Lei, Titus Neupert, Ziqiang Wang, Hsin Lin, Zahid Hasan We recently found that the kagome magnet can have giant spinorbit tunability (Nature 562, 91–95 (2018)). We use STM/S to elucidate the atomically resolved electronic states and their magnetic response in another transition metal based kagome magnet. We determine the chemical nature of the surface by atomic imaging of the native defects and surface step edges. On different surface terminations, we have observed different types of tunneling spectra, which corresponds well with our first principle calculation. Surprisingly, we find the tunneling signal has systematic magnetic field response, demonstrating an intriguing coupling of electronic structure and magnetism in a frustrated setting. We further discuss the connection of these results with the topological fermions and Berry phase theory. 
Tuesday, March 5, 2019 11:51AM  12:03PM 
F04.00004: Evidence for edge states in trigonal layered PtBi_{2} Xiaoang Nie, Youguo Shi, Hao Zheng, Jinfeng Jia PtBi_{2} is predicted to be a 3D topological semimetal which possesses triply degenerate point close to Fermi level. Here, we observe that unpredicted edge states exist at the edge of PtBi_{2} using scanning tunneling microscopy at 4.2K. More importantly, due to the inversion symmetry breaking, PtBi_{2} features two inequivalent top and bottom surfaces. We detect the edge states at the step edges on both surfaces. 
Tuesday, March 5, 2019 12:03PM  12:15PM 
F04.00005: Evidence of Charge density wave in Re doped MoTe_{2} Suman Kamboj, Anshu Sirohi, Aastha Vasdev, Manasi Mandal, Sourav Marik, Ravi Prakash Singh, Goutam Sheet Transition metal dichalcogenides exhibit interesting structural and intercalation chemistry and consequent exotic physical properties. Superconductivity with a very low transition temperature of 0.1 K was earlier discovered in the orthorhombic MoTe_{2}. MoTe_{2} also shows a charge density wave (CDW) phase when grown in thin film form, but a CDW phase in bulk MoTe_{2} has not been reported. It is also known that Re substitution for Mo sites leads to an increase in superconducting transition temperature. Mo_{0.8}Re_{0.2}Te_{2 }shows a high critical temperature T_{c} of 3.8 K. Based on our transport and scanning tunneling microscopy experiments we will discuss that the compound Mo_{0.8}Re_{0.2}Te_{2} also supports a CDW phase with an onset temperature of 150 K. Our results suggest that CDW and superconductivity may compete with each other in Re doped MoTe_{2}. 
Tuesday, March 5, 2019 12:15PM  12:27PM 
F04.00006: Topological Appearances between Two TypeII Weyl Semimetals Chunliang Lin Topology in abstract mathematics has revolutionized our conventional understanding of condensed matter physics, resulting in the emergence of exotic quantum phases such as topological insulators (TIs). Current realizations of the Weyl semimetals (WSMs) leads us to futher study the topological phases of matter beyond TIs. WSMs have gathered great attentions because the quasiparticles in WSMs behave as Weyl fermions, massless chiral fermions. WSMs are classified into Type I and II, according to the topology of the Weyl point, where the electron and hole pockets touch each other. Quasiparticle interference (QPI) study with STM has shown the evidence that a T_{d} phase Tungsten Ditelluride (WTe_{2}) is typeII WSM^{<span style="fontsize:10.8333px">1)</span>}, agreeing with the prior theoretical predictions. A similar measurement has also been performed to a T_{d} phase Molybdenum Ditelluride (MoTe_{2})^{2)}. The difference in the topological appearance (i.e. the positions of the Weyl points and the Fermi arc surface states) of MoTe_{2 }from that of WTe_{2} is clearly revealed. 
Tuesday, March 5, 2019 12:27PM  12:39PM 
F04.00007: Andreev reflection and Josephson currents on the surface of line Weyl semimetals Xiang Hu, Dmitry Pikulin, Enrico Rossi We study the Andreev reflection of line Weyl semimetals' surfaces drumhead states. Drumhead states are expected to have a very large effective mass. We show that the measurement of the Andreev reflection can be a very effective way to detect such mass experimentally. 
Tuesday, March 5, 2019 12:39PM  1:15PM 
F04.00008: Observation of the nonlinear Hall effect in bilayer WTe2 Invited Speaker: Suyang Xu The electrical Hall effect is the production of a transverse voltage under an outofplane magnetic field. In nonmagnetic materials without external magnetic fields, the electrical Hall effect is rarely explored because of the constraint by timereversal symmetry. However, only the Hall effect in the linear response regime identically vanishes due to timereversal symmetry. The Hall effect in the nonlinear response regime, on the other hand, may not be subject to such symmetry constraints. Here, we report the observation of the nonlinear Hall effect (NLHE) in the electrical transport of the nonmagnetic 2D quantum material, bilayer WTe2. The NLHE exhibits unusual properties sharply distinct from the AHE in metals: The NLHE shows a quadratic IV characteristic; It strongly dominates the nonlinear longitudinal response, leading to a Hall angle of about 90 deg. We further show that the NLHE directly measures the “dipole moment” of the Berry curvature, which arises from layerpolarized Dirac fermions in bilayer WTe2. Our results demonstrate a new Hall effect and provide a powerful methodology to detect Berry curvature in a wide range of nonmagnetic quantum materials in an energyresolved way. 
Tuesday, March 5, 2019 1:15PM  1:27PM 
F04.00009: Giant anomalous Hall and planar Hall effect in magnetic Weyl semimetal Co_{3}Sn_{2}S_{2 }nanoflakes ShuoYing Yang, Enke Liu, Claudia Felser, Stuart S Parkin Weyl fermions are chiral massless fermions manifested in crystalline solids by spin split conduction and valence bands crossing at discrete points. Magnetic Weyl semimetals with spontaneous timereversalsymmetrybreaking are predicted to host large Berry curvature and resulting in a large intrinsic anomalous Hall effect (AHE). In this work, we perform detailed transport studies on the nanoflake devices of magnetic Weyl semimetal, Co_{3}Sn_{2}S_{2}. The twodimensional nature of its Kagomelattice allows Co_{3}Sn_{2}S_{2} to be grown into nanoflakes as thin as 180 nm via the chemical vapor transport method. Through magnetotransport measurements, we observe a large intrinsic anomalous Hall conductivity (AHC) and anomalous Hall angle (AHA) generated by the Weylrelated Berry curvature that is robust against both temperature and charge conductivity. The AHC and AHA simultaneously reach 1422 S/cm and 23%, even higher than recent reports in single crystals [1]. Furthermore, we discuss the observation of the planar Hall effect (PHE) in Co_{3}Sn_{2}S_{2} which can be caused by the chiral anomaly. Other possible origins of the PHE, including contributions from orbital magnetoresistance and interaction of the electrons with the magnetic order will also be discussed. 
Tuesday, March 5, 2019 1:27PM  1:39PM 
F04.00010: Origin of the finitetemperature violation of the WiedemannFranz law in semimetals Alexandre Jaoui, Benoit Fauque, Kamran Behnia We present a study of the electrical and thermal conductivities of the semimetals WP_{2}, WTe_{2} and Sb in the 2K40K temperature range. At low temperature, the WiedemannFranz law holds (κ/T = L_{0}/ρ with κ the thermal conductivity, ρ the electrical resistivity and L_{0} the Lorenz number). However, upon warming, a downward deviation from the WiedemannFranz law is observed. In the case the Weyl semimetal WP_{2} [1], the difference reaches an exceptionally large value compared to what we determined in WTe_{2} and Sb and what was previously reported in other metals [2]. We identify electronelectron scattering as the origin of this departure [3]. We were further able to quantify the mismatch in the frequency of interelectronic collisions which conserve momentum (i.e. electric current) but degrade energy (as in the case of normalstate liquid ^{3}He). This sets a narrow temperature window between the ballistic and diffusive regimes where the hierarchy of scattering times corresponds to the hydrodynamic requirements for charge carriers [4]. 
Tuesday, March 5, 2019 1:39PM  1:51PM 
F04.00011: Lowdissipation edge currents without edge states Giovanni Vignale, Justin C. W. Song We show that bulk free carriers in topologically trivial multivalley insulators with nonvanishing Berry curvature give rise to lowdissipation edge currents, which are squeezed within a distance of the order of the valley diffusion length from the edge. This happens even in the absence of edge states [topological (gapless) or otherwise], and when the bulk equilibrium carrier concentration is thermally activated across the gap. 
Tuesday, March 5, 2019 1:51PM  2:03PM 
F04.00012: Microwave electrodynamics of WP_{2} James Day, Graham Baker, Vicky Süß, Chandra Shekhar, Claudia Felser, Douglas Bonn We report on measurements of the microwave conductivity of WP_{2} from 0.5 to 20 GHz and at low temperatures by way of bolometric broadband microwave spectroscopy. WP_{2} is a recently discovered typeII Weyl semimetal that has been reported to host several anomalous transport properties, including a recordhigh residual resistivity ratio and magnetoresistance. Recent studies of the temperaturedependent electrical and thermal conductivities of WP_{2} show that, at certain temperatures, electronic transport is in the hydrodynamic regime – in stark contrast to the diffusive transport found in most metals. Identification of the various scattering rates has thus far relied on measurement of DC quantities, whereas key signatures of charge dynamics are also manifested in the frequency dependence of these quantities. We will discuss our measurements of the microwavefrequency electrical conductivity in the context of hydrodynamic electronic transport in WP_{2}. 
Tuesday, March 5, 2019 2:03PM  2:15PM 
F04.00013: NMR Investigation of the Weyl Semimetal TaAs Arash AkbariSharbaf, Aimé Verrier, Nityan Nair, James G. Analytis, Jeffrey Quilliam Weyl semimetals are expected to host topologically protected bulk states. Recently ^{181}Ta nuclear quadrupolar resonance (NQR) was used as a bulk probe to investigate the band structure of the Weyl semimetal TaP near the Weyl nodes. [1] This is possible because nuclear spins couple to Weyl fermions via an anomalous hyperfine coupling influencing the temperaturedependent nuclear spin relaxation time T_{1}. [2] Depending on the position of the chemical potential with respect to the Weyl nodes, the temperaturedependent relaxation rate is expected to deviate from the Korringa relation, where 1/T_{1}T = constant. In this work we present ^{181}Ta nuclear magnetic resonance (NMR) study of a single crystal TaAs Weyl semimetal, a material in which the chemical potential is typically closer to the Weyl nodes. The 1/T_{1}T dependence of the ±3/2 <> ±5/2 transition is measured using progressive saturation, and results are compared to theoretical calculations [2] and results on TaP [1]. The ^{181}Ta quadrupole parameters and Knight shift are also determined from the field and temperature dependence of the resonance frequency. 
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. 
© 2022 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700