Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session X44: Dirac and Weyl Semimetals: Transport IIIFocus

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Sponsoring Units: DMP Chair: Tiang Liang, Stanford University Room: 391 
Friday, March 17, 2017 8:00AM  8:12AM 
X44.00001: Exotic quantum properties under high magnetic fields and pressureinduced superconductivity in layered ZrTe$_{\mathrm{5}}$ and pyrite PtBi$_{\mathrm{2}}$ Mingliang Tian, Zhaorong Tian, Wei Ning Topological Dirac semimetal is a newly discovered class of materials which has attracted intense attention. This material can be viewed as a threedimensional (3D) analog of graphene and has linear energy dispersion in bulk, leading to a range of exotic transport properties. Here we report direct quantum transport evidence of the 3D Dirac semimetal phase of semimetallic materials ZrTe$_{\mathrm{5}}$ and pyrite PtBi$_{\mathrm{2}}$ by angulardependent magnetoresistance measurements under high magnetic fields up to 35 T, as well as the pressureinduced superconductivity. We observed very clear negative longitudinal magnetoresistance in ZrTe5 induced by chiral anomaly under the condition of the magnetic field aligned only along the current direction, and the extreme large unsaturated magnetoresistance in pyrite PtBi$_{\mathrm{2}}$ up to 11.2 million percent at T $=$ 1.8 K and 33 T, which surpasses the previously reported Dirac materials, such as LaSb, WTe$_{\mathrm{2}}$ and NbP. Analysis of the Shubnikov de Haas oscillations suggest that both ZrTe$_{\mathrm{5}}$ and PtBi$_{\mathrm{2\thinspace }}$are likely a new topological semimetals. [Preview Abstract] 
Friday, March 17, 2017 8:12AM  8:24AM 
X44.00002: Quantum Oscillations at Integer and Fractional Landau Level Indices in ZrTe5 Wenlong Yu, Yuxuan Jiang, Jeremy Yang, Zhiling Dun, Haidong Zhou, Zhigang Jiang, Ping Lu, Wei Pan A threedimensional (3D) Dirac semimetal (DS) is an analogue of graphene, but with linear energy dispersion in all (three) momentum directions. We report here the results in exfoliated ZrTe$_{\mathrm{5}}$ thin flakes from the studies of scanning transmission electron microscopy and low temperature magnetotransport measurements. Several unique results were observed. First, a $\pi $ Berry phase was obtained from the Landau fan diagram. Second, the longitudinal resistivity shows linear magnetic field dependence. Most surprisingly, quantum oscillations were also observed at fractional Landau level indices N $=$ 5/3 and 7/5, demonstrating strong electronelectron interaction effects in ZrTe$_{\mathrm{5}}$. [Preview Abstract] 
Friday, March 17, 2017 8:24AM  8:36AM 
X44.00003: Transport properties and ARPES measurements of the Dirac linenode semimetals CaTX Eve Emmanouilidou, Bing Shen, Aoshuang Shi, Ni Ni, Chang Liu, Xiaoyu Deng, Gabriel Kotliar, Suyang Xu Recently noncentrosymmetric CaAgAs crystallizing in the P6 2m space group has been proposed to be a topological linenode semimetal with only nontrivial bands near the Fermi level. In this talk we present magnetotransport properties, ARPES measurements and DFT calculations of single crystalline CaAgAs and its sister compound CaCdGe. At 2K and 9 T, linear transverse magnetoresistance (MR) up to 18{\%} is observed in CaAgAs while extremely large nonsaturating quadratic MR up to 2500{\%} shows up in CaCdGe, attributing to the electronhole compensation revealed by Hall measurements. This is consistent with the DFT calculation which reveals two hole and one electron Fermi pockets in CaCdGe. Angledependent Shubnikovde Haas oscillations in CaCdGe resolve one of the hole Fermi pockets revealed by DFT. ARPES measurements on both compounds will be discussed too. [Preview Abstract] 
Friday, March 17, 2017 8:36AM  9:12AM 
X44.00004: Phase transition in the quantum limit of the Weyl semimetal TaAs Invited Speaker: Brad Ramshaw Under extreme magnetic fields, electrons in a metal are confined to a single highlydegenerate quantum state$$a regime known as the quantum limit. This state is unstable to the formation of new states of matter, such as the fractional quantum Hall effect in two dimensions. The fate of 3D metals in the quantum limit, on the other hand, has been relatively unexplored. The discovery of monopnictide Weyl semimetals has renewed interest in the highfield properties of 3D electrons, particularly those with linear dispersions. Several difficulties in determining the highfield properties have arisen, including the highly anisotropic nature of the magnetoresistance, and the presence of trivial (parabolic) Fermi pockets that cloud the underlying behaviour of Weyl pockets. We use magnetic fields up to 90 Tesla to put the Weyl semimetal TaAs into its extreme quantum limit, isolating its linear 0$^{\mathrm{th}}$ Landau level from the rest of the electronic spectrum. We find that a gap opens in the conductivity parallel to the magnetic field above 70 Tesla, and also find an abrupt reversal in the fieldevolution of the sound velocity at the same magnetic field, suggesting a thermodynamic phase transition to a new state of matter. [Preview Abstract] 
Friday, March 17, 2017 9:12AM  9:24AM 
X44.00005: dHvA oscillations in nodalline semimetals ZrSiM (M$=$S,Se,Te) Jin Hu, Zhijie Tang, Jinyu Liu, Yanglin Zhu, Zhiqiang Mao The breakthrough in the discovery of topological semimetals provides opportunities to explore the exotic properties of relativistic fermions in condensed matter. Among those materials, the Dirac nodalline semimetal represents a new type of topological quantum state which displays Dirac cones along a one dimensional line, in contrast with the Dirac or Weyl semimetals with discrete Dirac or Weyl cones. Here we report the quantum oscillation studies on the nodalline semiemtals ZrSiS, ZrSiSe, and ZrSiTe. We have observed very strong dHvA oscillations in these materials, which provides an ideal opportunity to study their properties of Dirac states. In ZrSiS, we found distinct properties associated with the novel Dirac state protected by nonsymmorphic symmetry which was previously probed by ARPES experiments: the 2D Dirac cone state exhibits particularly strong Zeeman splitting at low fields. In ZrSiSe and ZrSiTe, we have provided evidence for nodalline fermions in these materials, and revealed the evolution of band structure toward 2D from ZrSiS to ZrSiSe and to ZrSiTe. In addition, we have demonstrated that their atomically thin crystals are accessible via mechanical exfoliation, which raises the possibility of realizing the theoretically predicted 2D topological insulators. [Preview Abstract] 
Friday, March 17, 2017 9:24AM  9:36AM 
X44.00006: Exploring consequences of Dirac nodal lines in ternary semimetal ZrSiS by angledependent magneto electrical transport measurements Yixuan Chen, Justin Rodriguez, Brian Zakrzewski, Zhijie Tang, Jin Hu, Zhiqiang Mao, Ying Liu ARPES, de Haasvan Alphen and Shubnikov de Haas quantum oscillation studies of ZrSiS have revealed that this ternary semimetal hosts Dirac nodal line fermions through the determination of a nontrivial Berry phase. Interesting behavior was observed in the magnetoresistance measurements including a butterflyshaped angle dependence as the magnetic field is tilted away from the $c$ axis. We studied the consequences of Dirac line nodes in the electrical transport properties of this material by carrying out systematic angledependent magnetoresistance and Hall coefficient measurements. The effects of the existence of the zeroth Landau level when the field is aligned in the Dirac nodal line plane will be discussed. [Preview Abstract] 
Friday, March 17, 2017 9:36AM  9:48AM 
X44.00007: A layered Dirac system candidate: Fermi surface and anomalous Berry phase in ZrSiSe YuChe Chiu, KuanWen Chen, David Graf, Qiong Zhou, Thomas J. Martin, Julia Y. Chan, Michelle Johannes, Ryan E. Baumbach, Luis Balicas ZrSiSe was recently claimed to correspond to a novel type of nodal Dirac system. We synthesized single crystals through a combination of solid state reaction and chemical vapor transport. The asgrown single crystals display residual resistivities on the order of 100 nOhmcm at 2K yielding a resistivity ratio surpassing 200. Magnetoresistance (MR) measurements reveal a nonsaturating increase in the resistivity by a factor of 500000{\%} under fields up to 35 Tesla. De Haas van Alphen measurements under high magneticfields reveal a Fermi surface that is more complex than previously reported, although its geometry generally agrees with band structure calculations that indicate Diraclike dispersion in the bulk around the Fermi energy. The charge carrier effective masses extracted from LifshitzKosevich (LK) fits to the amplitude of quantum oscillations were found to range between 0.08me to 0.5me where me is the free electron mass. Fittings of the oscillatory signal to the LK formalism further reveal the existence of cyclotron orbits displaying nontrivial Berry phases approaching pi, which is consistent with the expectations from band structure calculations. [Preview Abstract] 
Friday, March 17, 2017 9:48AM  10:00AM 
X44.00008: Probing the electronic state in the strong topological metals Zr$_{2}$Te$_{2}$P, Hf$_{2}$Te$_{2}$P, and Zr$_{2}$Te$_{2}$As and their structural analogue Ti$_{2}$Te$_{2}$P K.W Chen, N. Aryal, S. Das, D. Graf, S. Memaran, S. Zhang, J. Dai, E. Frantzeskakis, F. Fortuna, A. SantanderSyro, L. Balicas, E. Manousakis, R. Baumbach Recent work shows that Zr$_{2}$Te$_{2}$P is a strong topological metal with time reversal symmetry protected surface Dirac cones at the and points (in the hexagonal basis), bulk bands with a possible Diraclike character at the point, and conventional (quadratically dispersing) bulk electronic bands centered around the point. We report results for the broader family of materials $X_{2}$Te$_{2}M$ ($X=$ Ti, Zr, Hf, and $M =$ P, As), where we find remarkable agreement between the calculated electronic states and those measured through quantum oscillations in the magnetic torque. Analysis of the quantum oscillations additionally reveals small ($m$* \textless 0.1 $m_{e})$ charge carrier masses and nontrivial Berry phases for the Fermi surfaces at the point, and more conventional behavior for the bands that are centered around the point. These results will be discussed with attention to the relationship between topologically protected surface states and bulk metallic conduction. We also discuss prospects for designing new materials in this structure. [Preview Abstract] 
Friday, March 17, 2017 10:00AM  10:12AM 
X44.00009: Quantum oscillations study of the typeII Weyl semimetal candidate $\beta $MoTe$_{\mathrm{2}}$ R. Schoenemann, D. Rhodes, Q. Zhou, Q. Zhang, S. Das, E. Manousakis, L. Balicas, J. Chang, G. McCandless, E. Kampert, Y. Shimura, M. Johannes Here we present a quantum oscillations study of high quality single crystalline $\beta $MoTe$_{\mathrm{2}}$ samples that show residual resistivity ratios between 400 and 2000. We performed angular and temperature dependent Shubnikovde Haas (SdH) and de Haasvan Alphen (dHVA) measurements and compared our results with bandstructure calculations. The magnetoresistivity shows no sign of saturation and reaches values of approximately 10$^{\mathrm{6}}$ at 60 T and 1.7 K. Hall effect measurements indicate almost perfect electronhole compensation at low temperatures. Additionally we were able to extract a nontrivial Berry Phase from dHvA measurements, i.e. between 2$\pi \quad x$ 0.445 and 2$\pi $ x 0.475 which is close to the predicted value of $\pi $. In contrast to recent ARPES data, the Fermi surface obtained by our bulk measurements deviates significantly from the calculated band structure. Furthermore we observe broad anomalies in Hall and specific heat measurements that indicate an evolution of the electronic structure below 100 K which might be responsible for the observed discrepancies$^{\mathrm{2}}$. 2. Zhou, Q. et al. Phys, Rev. B \textbf{94}, 121101(R) (2016); arXiv:1605.09065[condmat.messhall] [Preview Abstract] 
Friday, March 17, 2017 10:12AM  10:24AM 
X44.00010: Transport properties of the Dirac typeII semimetal candidate PtTe$_2$ Qiong Zhou, Daniel Rhodes, YuChe Chiu, KuanWen Chen, Wenkai Zheng, Rico Sh{\"o}nemann, Erik Kampert, Tobias F{\"o}rster, Thomas Martin, Julia Chan, Luis Balicas We investigated the electronic structure and transport properties via the temperature and angular dependence of the Shubnikovde Haas (SdH) and de Haas van Alphen (dHvA) effect in single crystals of the semimetallic platinum ditelluride (PtTe$_2$), recently claimed to be a novel typeII Dirac semimetal. Our highquality PtTe$_2$ crystal displays nonsaturating and large magnetoresistance at magnetic field up to 9 T. The dHvA oscillation reveals up to 8 frequencies suggesting a rather complex Fermi surface with evidence for a nontrivial Berry phase. The crystal quality improved considerably under subsequent annealing at hightemperatures leading to the observation of linear in field magnetoresistivity. Combined with effective masses in the order of $\sim 0.1$ free electron mass, these results further suggest that PtTe$_2$ displays bulk Diraclike bands. Halleffect measurements suggest that this compound is not a compensated semimetal. [Preview Abstract] 
Friday, March 17, 2017 10:24AM  10:36AM 
X44.00011: Angledependent Shubnikovde Haas quantum oscillation in the topological semimetal YPtBi Hyunsoo Kim, Halyna Hodovanets, Kefeng Wang, Johnpierre Paglione Noncentrosymmetric cubic YPtBi is a topological semimetal with strong spinorbit coupling and resultant $j$ = 3/2 conduction fermions that make this superconductor with $T_c$ = 0.8 K the first candidate superfluid with highspin (i.e. beyond spintriplet) Cooper pairing. To develop a realistic pairing model, we investigate the Fermi surface geometry and fundamental properties of the nontrivial conduction fermions in YPtBi using temperature and fielddependent quantum oscillations measurements of the angledependent Shubnikovde Haas (SdH) oscillations. We will present our analysis of angledependent frequency and amplitude of the SdH oscillations, and discuss the details of the normal state Fermiology of this exotic system. [Preview Abstract] 
Friday, March 17, 2017 10:36AM  10:48AM 
X44.00012: Transport behavior and quantum oscillation study of typeII Dirac semimetal VAl3 Kefeng Wang, Limin Wang, D. Graf, D Campbell, J Paglione We report highquality singlecrystal synthesis and characterization of the proposed typeII Dirac semimetal VAl3, reviewing transport experiments performed up to 34 T magnetic fields. Up to high fields, VAl3 exhibits an unsaturating magnetoresistance, with multiband behavior consistent with the coexistence of light holes and heavy electrons. We will review quantum oscillations measurements from torque magnetometry experiments and compare the Fermi surface geometry with electronic structure calculation, discussing twodimensional behavior of a very small frequency oscillation that may be assigned to surface states in this Dirac semimetal. [Preview Abstract] 
Friday, March 17, 2017 10:48AM  11:00AM 
X44.00013: De Haasvan Alphen quantum oscillations in LuSn$_{2}$ Yanglin Zhu, Jin Hu, David Graf, Zhiqiang Mao We have successfully synthesized single crystals of binary compound LuSn$_{2}$ and observed strong De Haasvan Alphen (dHvA) quantum oscillations with three oscillation frequencies ($F_{\alpha } \quad =$ 70T, $F_{\beta \, }=$ 422T and $F_{\gamma } \quad =$ 511T for H//c) in this material. From the analyses of dHvA oscillations, the quasiparticles of this material are found to be very light (m$_{\alpha \, }=$ 0.053 m$_{0}$, m$_{\beta \, }=$ 0.067 m$_{0,\, }$m$_{\gamma } \quad =$ 0.072 m$_{0,}$ where m$_{0}$ is the mass of a bare electron) and possess high quantum mobility (2500 cm$^{2}$/VS for $F_{\alpha \, }$band). For the $F_{\alpha }$ component, the evidence of nontrivial Berry phase was also revealed from the fit the of the oscillation pattern to the LifshitzKosevich formula which takes Berry phase into account for a topological material. The angular dependence of $F_{\alpha }$ indicates the $F_{\alpha }$ band is quasitwo dimensional. These observations imply possible existence of a quasi2D bulk Dirac state in LuSn$_{2}$. This result calls for further verification by firstprinciple calculations and ARPES experiments. [Preview Abstract] 
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