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 W44: Dirac and Weyl Semimetal: TransportFocus
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Sponsoring Units: DMP Chair: William Meier, University of Tennessee Room: Room 316 |
Thursday, March 9, 2023 3:00PM - 3:36PM |
W44.00001: Spin-valley locking, bulk quantum Hall effect and nonlinear Hall effect in a noncentrosymmetric Dirac material Invited Speaker: Zhiqiang Mao Spin-valley locking in the band structure of monolayers of MoS2 and other group-VI transition metal dichalcogenides (TMDCs) has attracted enormous interest, since it offers potential for valleytronic and optoelectronic applications. Such an exotic electronic state has sparsely been seen in bulk materials. In this talk, I will report a bulk spin-valley locked electronic state in a 3D non-centrosymmetric Dirac material BaMnSb2 [1]. Such a state is revealed by comprehensive studies using first principles calculations, tight-binding and effective model analyses, angle-resolved photoemission spectroscopy measurements. Moreover, this material also exhibits a stacked quantum Hall effect (QHE). The spin-valley degeneracy extracted from the QHE is close to 2. This result, together with the Landau level spin splitting, further confirms the spin-valley locking picture in BaMnSb2. Recently, we also found such a spin-valley locked state leads to a bulk intrinsic nonlinear Hall effect at room temperature [2], which is characterized by alternating current driven second-harmonic and rectified Hall voltage response under time-reversal symmetry conditions. These findings broaden the coupled spin and valley physics in 2D systems into a 3D system. |
Thursday, March 9, 2023 3:36PM - 3:48PM |
W44.00002: Field-direction dependent quantum-limit magnetoresistance in correlated Dirac semimetal CaIrO3 Rinsuke Yamada, Jun Fujioka, Minoru Kawamura, Shiro Sakai, Motoaki Hirayama, Ryotaro Arita, Tatsuya Okawa, Daisuke Hashizume, Ryosuke Kurihara, Masashi Tokunaga, Yoshinori Tokura The electron correlation in topological semimetals has been an important subject in topological material physics. The quantum confinement of strongly correlated relativistic electrons into quasi-one-dimension under a strong magnetic field (B) offers a fertile ground for exploring the emergent correlated topological phenomena, but has been rarely realized so far. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W44.00003: Anomalous Hall effect in HfTe5 thin flakes Robert A Welser, Jinyu Liu, David E Graf, Michael T Pettes, Javier D Sanchez-Yamagishi, Luis A Jauregui Van der Waals (vdW) type topological materials provide a unique platform for studying what the role of dimensionality effect is played on topological properties. Topological pentatellurides, with a vdW layered structure, have been shown to display a lot of intriguing quantum transport properties in the bulk form. Here we report on the magnetotransport properties of HfTe5 thin flakes We fabricate the HfTe5 thin flake devices, with a thickness ranging from 90 nm to 280 nm, inside an argon filled glove-box and cap the samples with hBN to ensure that the sample quality is pristine. We observe the anomalous Hall effect (AHE) that evolves with temperature and sample thickness in all of the thin flake devices. The anomalous Hall effect remains persistent in the presence of high magnetic fields. We have tried different models to fit longitudinal and Hall conductivity. The AHE we have observed is likely due to a nontrivial Berry curvature caused by Zeeman spin splitting of the massive Dirac bands. Our magnetotransport results give new insight into how the Zeeman effect influences the topological band in HfTe5. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W44.00004: Chiral anomaly across the Lifshitz transition in ZrTe5 Pedro Mercado, Genda Gu, Qiang Li A key property of Weyl and Dirac semimetals is the near conservation of chiral charge. The presence of collinear electric and magnetic fields leads to the non-conservation of chiral charge density through the chiral anomaly. Given the strong Berry curvature and near conservation of chiral charge in Weyl and Dirac semimetals, the chiral anomaly can give rise to measurable effects such as the chiral magnetic effect (CME) and the planar Hall effect (PHE). In this work, we study the chiral anomaly across the temperature-induced Lifshitz transition, in which the Fermi level goes from the conduction to the valence band with increasing temperature, by performing measurements of the CME and PHE in ZrTe5 in a broad temperature range and high magnetic fields. Our results provide insight into the effect of the Lifshitz transition on the chiral anomaly in topological semimetals. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W44.00005: Non-monotonic temperature dependence of the thermal chiral anomaly in Bi(1-x)Sb(x) Weyl semimetals below 10K Minyue Zhu, Dung D Vu, Joseph P C Heremans, Joonsang Kang The chiral anomaly has been shown in the electrical and thermal conductivity in ideal Weyl semimetals induced by a magnetic field in Bi(1-x)Sb(x) alloy single crystals that are topological insulators in zero field. [1] The crystals have mobilities at 10 K in the 1,000,000 to 3,000,000 range, and carrier concentrations around 10^15 cm^-3, indicating that the chemical potential is at the Weyl points and that there are no trivial pockets to the Fermi surface. In those samples, the anomalous thermal conductivity, obtained with the field along the trigonal direction, has a maximum at 40 K due to a combination of a T^1 law due to the anomaly and a decrease in inter-Weyl-point scattering above about 50 K. This theory predicts a monotonic decrease of the anomalous conductivity proportional to T at T<40 K. Here, we extend the thermal conductivity measurements of single crystal Bi(1-x)Sb(x) alloys to 2K. We report new experimental data that show a second maximum of thermal chiral anomaly at T= 4K. The anomalous thermal conductivity at 4K is about one order of magnitude larger than the theory predicts. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W44.00006: Unconventional Resistivity Scaling in Topological Semimetal CoSi Hsin Lin, Shang-Wei Lien, Ion Garate, Utkarsh Bajpai, Cheng-Yi Huang, Chuang-Han Hsu, Yi-Hsin Tu, Nicholas A Lanzillo, Arun Bansil, Tay-Rong Chang, Gengchiau Liang, Ching-Tzu Chen Nontrivial band topologies in semimetals lead to robust surface states that can contribute dominantly to the total conduction. This may result in reduced resistivity with decreasing feature size contrary to conventional metals, which may highly impact the semiconductor industry. Here we study the resistivity scaling of a representative topological semimetal CoSi using realistic band structures and Green’s function methods. We show that there exists a critical thickness dc dividing different scaling trends. Above dc, when the defect density is low such that surface conduction dominates, resistivity reduces with decreasing thickness; when the defect density is high such that bulk conduction dominates, resistivity increases as in conventional metals. Below dc, the persistent remnants of the surface states give rise to decreasing resistivity down to the ultrathin limit, unlike in topological insulators. The observed CoSi scaling can apply to broad classes of topological semimetals, providing guidelines for materials screening and engineering. Our study shows that topological semimetals bear the potential of overcoming the resistivity scaling challenges in back-end-of-line interconnect applications. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W44.00007: Unconventional Resistivity Scaling in Polycrystalline NbP Thin Films Asir Intisar Khan, Xiangjin Wu, Byoungjun Won, Emily R Lindgren, Christopher Perez, Kenneth E Goodson, Yuri Suzuki, Il-Kwon Oh, H.-S. Philip Wong, Eric Pop The electrical resistivity of ultrathin metal films increases with decreasing thickness due to electron scattering from the film surfaces. This behavior limits the performance of all modern nanoelectronics which include metal-based interconnects [1]. Here, topological Weyl semimetals (TWS) with their disorder-tolerant conductive surface charge states can be useful at the ultrathin film limit [2, 3]. However, for nanoelectronics applications, ultrathin TWS films need to be explored using industry-compatible deposition methods and temperatures. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W44.00008: Nonlinear Hall Effects in Weyl Semimetal Thin Films Ruihao Li, Shulei Zhang Weyl semimetals (WSMs) are a gapless topological phase that have attracted great attention in the past decade or so. The study of the bulk properties of WSMs has led to fruitful discoveries such as negative magnetoresistance, planar Hall effect, etc. More recently, there have been intense efforts in investigations beyond the linear transport regime, leading to proposals of nonlinear Hall effect of different origins, such as the Berry curvature dipole [1] and the chiral anomaly [2]. On the other hand, due to its unique band topology, the Fermi arc states emerge on the surfaces of a WSM, which are distinct from the surface states of gapped systems such as topological insulators. In this work, we will focus on the nonlinear Hall effects in WSM thin films in which the surface states are expected to play a more important role in charge transport due to large surface-to-volume ratio. In particular, we will employ a tight-binding model of a WSM and demonstrate how the Fermi arc states impact the chiral-anomaly-induced nonlinear Hall response under parallel electric and magnetic fields. In addition, we will also discuss how diffusion, which becomes prominent in the thin film geometry, can lead to modifications in nonlinear Hall effects of WSMs. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W44.00009: Investigation of nonlinear Hall effect induced by Berry Curvature dipole in a topological semimetal Ji-Eun Lee, Yu Liu, Minseong Kwon, Jinwoong Hwang, Minhyun Cho, Dong-Soo Han, Jun Woo Choi, Young Duck Kim, Zhi-Xun Shen, Sung-Kwan Mo, Cedomir Petrovic, Choongyu Hwang, Se Young Park, Chaun jang, Hyejin Ryu The Hall effects in a quantum system, such as quantum Hall effect (QHE) and quantum anomalous Hall effect (QAHE) have become an essential topic in condensed matter physics. Recently, a new type of Hall effect has been found in topological semimetals possessing a time-reversal symmetry in which the Hall conductivity is proportional to the square of the driving current. This unusual Hall signal is resulting from Berry curvature dipole (BCD) allowed from broken inversion symmetry. In this presentation, we discuss electronic and transport properties of a topological semimetal exhibiting BCD-induced nonlinear Hall effect using angle-resolved photoemission spectroscopy, first-principles calculations, and transport measurements. We find the origin of the substantial BCD hotspots contributed from the partially occupied spin-orbit split bands. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W44.00010: Thermopower of Nodal line Semimetals in a Magnetic Field Poulomi Chakraborty, Brian J Skinner, Aaron Hui We consider the thermoelectric response of a nodal line semimetal as a function of temperature T and applied magnetic field B. In the semiclassical limit of low magnetic field, we find that magnetic field can provide a large enhancement of the peak value of thermopower as a function of temperature. In the extreme quantum limit of magnetic field, where only one Landau level is occupied, the thermopower can achieve a very large value that increases linearly with B and is independent of T. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W44.00011: p x n-Type Transverse Thermoelectrics in a Type-II Weyl Semimetal TaIrTe4 Cheng-Chien Chen, Joshua C Mutch, Wei-Chih Chen, Cheng-Yi Huang, Paul T Malinowski, Jiun-Haw Chu p x n-type materials refer to materials with a p-type Seebeck coefficient in one direction and a n-type coefficient in the orthogonal direction. This type of materials allows for a transverse thermoelectric response, which is highly desirable for energy applications. Here, we report the observation of p x n-type behavior in TaIrTe4, a type-II Weyl semimetal, with an in-plane thermopower anisotropy Sxx-Syy reaching a maximum value 40 μV/K at 200 K. Intriguingly. we found that such a p x n-type behavior is absent in the similar compound NbIrTe4. The presence and absence of p x n-type behavior in these two materials are consistent with density functional theory calculations, which further predict that the thermopower anisotropy in both compounds can be enhanced up to 130 μV/K by electron doping. Such a strong thermopower anisotropy originates from the presence of both p-type and n-type carriers, each with high mobility in one direction. These results suggest that although type-II Weyl semimetal phase does not guarantee the existence of p x n-type behavior, its unique band structure provides the ingredient to engineer and optimize this phenomenon. |
Thursday, March 9, 2023 5:36PM - 5:48PM |
W44.00012: Transport Evidence of Weyl Orbit in Dirac Semimetal ZrSiSe Arash Fereidouni, Ashby Philip John, Krishna Pandey, Rabindra Basnet, Jin Hu, Hugh O Churchill Symmetry-protected Dirac semimetals show linear dispersion described by two copies of the Weyl equation. At the surface of such a crystal, the broken translation symmetry creates topological surface states called Fermi arcs. These Fermi arcs result in a cyclotron motion known as Weyl orbits that connect Fermi arcs on top and bottom surfaces through the chiral bulk states, which can be apparent in Shubnikov-de Haas oscillations. Fast Fourier Transform of Shubnikov-de Haas oscillations in thin flakes of ZrSiSe, a nonsymmorphic Dirac semimetal, reveals the unexpected frequency of 140 T not related to any known surface (450 T) or bulk (220 T) Fermi surface. We show that this frequency has a 2D nature by providing angle dependence and thickness dependence of quantum oscillations. Angle dependence of the 140 T frequency follows cos-1(θ), in contrast to bulk frequency, 220 T, which shows no change with angle. In addition, thickness dependence shows that the amplitude ratio of the 140 T to 220 T components exponentially increases by decreasing the thickness. In addition, we provide a comparison of phase analysis of the 140 T with 220 T frequency that points to different origins of these frequencies. We speculate this 140 T frequency could arise from Weyl orbit oscillations that would be consistent with a Fermi arc with a length of 0.08 °A-1 in ZrSiSe. |
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