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 X51: Dirac and Weyl Semimetals: Materials and Modeling--Thin Films and NanostructuresFocus Live
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Sponsoring Units: DMP DCMP Chair: Qiang Li, Stony Brook University |
Friday, March 19, 2021 8:00AM - 8:12AM Live |
X51.00001: Quantum Hall signature of Weyl orbits in dual-gated Dirac semimetal film Shinichi Nishihaya, Masaki Uchida, Yusuke Nakazawa, Markus Kriener, Yasujiro Taguchi, Masashi Kawasaki Recent prediction and observation of quantum Hall effect in three-dimensional topological semimetals [1-3] have attracted growing attention on the novel transport phenomena exerted by an exotic orbit so-called Weyl orbit. The Weyl orbit interconnects two spatially-separated surface Fermi-arc states via bulk Weyl nodes. While previous reports have focused on the subtle bulk thickness dependence of Weyl orbits [2], experimental evidence of their unique spatial distribution with electrons looping between two opposite surfaces has been missing. In this talk, we report Weyl-orbit-induced intrinsic coupling between top and bottom surface states in the quantum Hall regime of a dual-gated Dirac semimetal film. In particular, the doubly-degenerate quantum Hall states exhibit simultaneous modulation by top and/or bottom electric fields. The characteristic plateau transition patterns observed in electric and magnetic field scans directly evidence that the quantized states are not based on two independently localized conventional surface orbits, but rather based on a pair of Weyl orbits formed across the two opposite surfaces. |
Friday, March 19, 2021 8:12AM - 8:24AM Live |
X51.00002: Toward the realization of chiral qubit: quantum computing with chirality Qiang Li, Dmitri E Kharzeev, JIGANG Wang The quantum chiral anomaly enables a non-dissipative current in the presence of chirality imbalance. We proposed to utilize the chiral anomaly for the designs of qubits potentially capable of operating at THz frequency and at room temperature. The proposed chiral qubit is a microscopic-scale ring made of a Weyl semimetal, with the and states corresponding to the symmetric and antisymmetric superpositions of chiral currents circulating along the ring clockwise and counter-clockwise. In this talk, we report our investigations into several topological control principles driven by quantum coherence and understanding the time dependence of topological phase transition. These investigations included an experimental demonstration of a unique phonon-assisted topological switching in a Dirac semimetal, and giant dissipationless topological photocurrent that carries the imprints of chirality of Weyl fermions under zero magnetic field. The experimental results are compared with the dynamic phonon driving Weyl phases given theoretically by employing first-principles and effective Hamiltonian methods. |
Friday, March 19, 2021 8:24AM - 8:36AM Live |
X51.00003: Magnetic Weyl semimetal Co3Sn2S2 thin flakes with high electron mobility and large anomalous Hall effect Yukako Fujishiro, Miuko Tanaka, Masataka Mogi, Yoshio Kaneko, Takamoto Yokosawa, Naoya Kanazawa, Susumu Minami, Takashi Koretsune, Ryotaro Arita, Seigo Tarucha, Michihisa Yamamoto, Yoshinori Tokura Magnetic Weyl semimetals attract considerable interest not only for their topological quantum phenomena but also as an emerging materials class for realizing quantum anomalous Hall effect in the two-dimensional limit. In this work [1], we report a synthesis of high-quality thin flakes of magnetic Weyl semimetal Co3Sn2S2 by chemical vapor transport method. In 250nm-thick thin flake, we identify the largest electron mobility (~2,600 cm2V-1s-1) among magnetic topological semimetals, as well as the large anomalous Hall conductivity (~1,400 Ω-1cm-1) and anomalous Hall angle (~32 %) arising from the Berry curvature. The enhancement of electron mobility and Berry curvature will be discussed in terms of the effective hole doping. Our study provides a viable platform for studying high-quality thin flakes of magnetic Weyl semimetal and stimulate further research on unexplored topological phenomena in the two-dimensional limit. |
Friday, March 19, 2021 8:36AM - 8:48AM Live |
X51.00004: Importance of interactions for the band structure of the topological Dirac semimetal Na3Bi Iolanda Di Bernardo, James L Collins, Weikang Wu, Ju Zhou, Shengyuan Yang, Mark T Edmonds, Michael S Fuhrer We measured the band dispersions of topological Dirac semimetal Na3Bi using Fourier-transform scanning tunnelling spectroscopy to image quasiparticle interference (QPI) on the (001) surface of molecular beam epitaxy-grown Na3Bi thin films. We find that the velocities for the lowest-lying conduction and valence bands are significantly higher than previous theoretical predictions. We compare the experimental band dispersions to the theoretical band structures calculated using an increasing hierarchy of approximations of self-energy corrections due to interactions: GGA, meta-GGA, HSE06 and GW methods. We find that density functional theory methods generally underestimate the electron velocities. However, we find significantly improved agreement with an increasingly sophisticated description of the exchange and interaction potential, culminating in reasonable agreement with experiments obtained by GW method. The results indicate that exchange-correlation effects are important in determining the electronic structure of this Na3Bi, and are likely the origin of the high velocity. The electron velocity is consistent with recent experiments on ultrathin Na3Bi and also may explain the ultra-high carrier mobility observed in heavily electron-doped Na3Bi. |
Friday, March 19, 2021 8:48AM - 9:00AM Live |
X51.00005: Energy Dependence of the Circular Photogalvanic Effect in the Weyl Semimetal NbIrTe4 Seyyedesadaf Pournia, Giriraj Jnawali, Samuel M Linser, Iraj Abbasian Shojaei, Howard E Jackson, Leigh Smith, Congcong Le, Fu-Chun Zhang, Brenden Ortiz, Stephen D. Wilson We have investigated the Circular Photogalvanic Effect (CPGE) in the orthorhombic ternary compound, NbIrTe4. This material has been suggested theoretically as a type-II Weyl semimetal having 8 pairs of Weyl nodes, but no ARPES measurements have been published as yet. Measuring the photoresponse of a device fabricated from a thin film of this material (~100 nm thickness) under (0.3-1) eV illumination using a quarter-wave plate, reveals a clear energy dependent CPGE, increasing by as the photon energy approaches the Fermi energy. On top of this broad increase, there exists an energy resonance for the CPGE signal at ~0.6 eV. An underlying linear polarization-dependent photoresponse of the device from the photothermoelectric effect (PTE) is seen to decrease by an order of magnitude at lower energies. This PTE response has been measured in a broad energy range (0.3-1.8eV) using a linearly polarized light along two main crystal axes, and is in good agreement with DFT calculations. |
Friday, March 19, 2021 9:00AM - 9:12AM Live |
X51.00006: Proximity Effect Induced Topological Superconductivity in CeBi Thin Films Zhao Huang, Christopher Lane, Dmitry Yarotski, Antoinette Taylor, Jian-Xin Zhu Recently increasing evidence shows that magnetic CeBi can be a Weyl semimetal. With only one pair of Weyl nodes at low energies, CeBi serves as an interesting quantum material system to study various Weyl physics. In this work, we explore the possible emergence of topological superconductivity by sandwiching a CeBi thin film between two conventional superconductors like Niobium. After applying a magnetic field, CeBi can be in an antiferromagnetic, ferrimagnetic or ferromagnetic phase, which is coupled with the superconductors. We construct an accurate tight-binding multi-orbital Hamiltonian for CeBi from the first-principle electronic structure calculations. This enables us to get material-specific predictions on topological superconductivity. We obtain massless quasiparticle bands, which are chiral Majorana modes, when the CeBi is in the ferromagnetic phase. We anticipate that our theoretical results will provide a new platform of topological superconductivity arising from the Weyl materials, which is accessible to experimental observation. |
Friday, March 19, 2021 9:12AM - 9:24AM Live |
X51.00007: Coupling type II Weyl semimetal MoTe2 with a stronger s-wave superconductor: the competition with the inherent bulk superconducting condensate and the disloyal edge mode. Stephan Kim, Wudi Wang, Shiming Lei, Robert Cava, N. Phuan Ong We report the effects of coupling the type II Weyl semimetal MoTe2 with an s-wave superconductor that has a much larger superconducting gap. We fabricated nanodevices from exfoliated MoTe2 crystals (60 – 120 nm in thickness) with Nb electrodes. Tuning the temperature T and the perpendicular magnetic field B, we explored two different regimes. In one, the injected s-wave and the MoTe2 bulk condensates co-exist; in the other, only the injected condensate is present. Differential resistance (dV/dI) measurements revealed the competition of the two condensates. The transition from the superconducting state to the metallic state was stochastic, and the critical current Ic was greatly enhanced. In the absence of the MoTe2 bulk condensate, the injected condensate proximitized the edge mode of MoTe2. The differential resistance versus magnetic field spectra exhibited oscillations of critical current, where the area associated with the frequency corresponded to the physical area of the sample. |
Friday, March 19, 2021 9:24AM - 9:36AM Live |
X51.00008: Observation of the Dirac Semimetal Phase in MBE-grown ZrTe2 Thin Films with Tunable Source Laser-ARPES Max Stanley, Timothy S Pillsbury, Anthony R. Richardella, Yongxi Ou, Boyang Zheng, Hemian Yi, Jeffrey Rable, Danielle Reifsnyder Hickey, Nasim Alem, Vincent Henry Crespi, Cui-Zu Chang, Nitin Samarth Dirac semimetals (DSMs) have drawn a considerable amount of attention in recent years due to their linear, gapless bands near the Fermi level. The transition metal dichalcogenide ZrTe2 has been theoretically predicted and experimentally demonstrated to have such a DSM phase, although direct observation of linear dispersion in all three dimensions is yet unreported. Using molecular beam epitaxy, we have grown thin films of ZrTe2 on insulating sapphire substrates. The DSM phase of ZrTe2 is investigated by in-vacuo angle-resolved photoemission spectroscopy (ARPES). Using high harmonic generation from a Y-Fi laser, we vary the excitation wavelength of our ARPES experiment to observe the linear dispersion of the reported Dirac cone in all three momentum directions. Further, we examine the change in the DSM phase with the introduction of transition metals dopants. These create ferromagnetic order in ZrTe2, as confirmed by the square anomalous Hall hysteresis in transport measurements. |
Friday, March 19, 2021 9:36AM - 9:48AM Live |
X51.00009: Quantum transport in Dirac semimetal Cd3As2 thin films Run Xiao, Sayak Ghosh, Arpita Mitra, Wilson Yanez, Timothy S Pillsbury, Yawen Fang, Juan Chamorro, Santu Baidya, Tanya Berry, David Vanderbilt, Yi Li, Tyrel McQueen, Brad Ramshaw, Nitin Samarth The synthesis of thin films of the Dirac semimetal (DSM) Cd3As2 by molecular beam epitaxy (MBE) provides an attractive avenue for studying quantum transport in a DSM as a function of quantum confinement and chemical potential. We have used MBE to grow thin films of Cd3As2 on GaAs (111)B substrates with a GaSb buffer layer. The film thickness is varied in the range of 7 nm – 20 nm. Atomic force microscopy, x-ray diffraction, and electrical transport show that the films have good crystalline quality (root mean square surface roughness ~ 1.5 nm and full-width half maximum of rocking curves ~ 0.12°) and reasonable electron mobility (5,000 – 40,000 cm2/V.s at 4.2 K). We have studied Shubnikov-de Haas oscillations in lithographically patterned top gated Hall bar devices as a function of gate voltage, temperature, and magnetic field magnitude/angle. We interpret these quantum oscillation data in concert with in vacuo angle-resolved photoemission spectroscopy and first-principles calculations to gain insight into the Fermi surface of these DSM thin films. |
Friday, March 19, 2021 9:48AM - 10:00AM Live |
X51.00010: Fabrication and magnetotransport measurements of ZrSiSe/CrGeTe3 heterostructures Arash Fereidouni, Rabindra Basnet, Md Rafique Un Nabi, Jin Hu, Hugh O. H. Churchill Band crossings of topological materials are protected by crystal symmetry and time reversal symmetry. Breaking time reversal symmetry splits the Dirac cone into a pair of Weyl cones creating a new quantum anomalous Hall insulator state. We report the fabrication and transport measurements of ZrSiSe/CrGeTe3 heterostructures in which Hall bars are fabricated on thin flakes of ZrSiSe, an exfoliatable topological semimetal. To break time reversal symmetry, a few-layer flake of the 2D ferromagnet CrGeTe3 is transferred onto the ZrSiSe. Finally, the ZrSiSe is gated from the top using FeSe with an hBN insulation layer, which also prevents oxidation of the ZrSiSe. Transport measurements of ZrSiSe show quantum oscillations with frequency of 210 T and giant magnetoresistance of 1500%. We will discuss ongoing experiments as a function of gate voltage and compare heterostructures with and without the ferromagnetic layer. |
Friday, March 19, 2021 10:00AM - 10:36AM On Demand |
X51.00011: Electrical manipulation of a Weyl semimetallic state Invited Speaker: Satoru Nakatsuji Electrical manipulation of emergent phenomena due to nontrivial band topology is a key to realize next-generation technology using topological protection. Recent discovery of the magnetic Weyl fermions in the antiferromagnet Mn3Sn has attracted significant attention [1], as it exhibits various exotic phenomena with robust properties due to the Weyl nodes [2-6]. Given the prospects of antiferromagnetic (AF) spintronics for realizing high-density devices with ultrafast operation, it would be ideal if one could electrically manipulate an AF Weyl semimetal. Here we demonstrate the electrical switching of a Weyl semimetal state and its detection by anomalous Hall effect (AHE) [7]. In particular, we employ a polycrystalline thin film of the AF Weyl metal Mn3Sn. Using the bilayer device of Mn3Sn and nonmagnetic metals (NMs), we find that an electrical current density of ~1010-1011 A/m2 in NMs induces the magnetic switching with a large change in Hall voltage, and besides, the current polarity along a bias field and the sign of the spin Hall angle of NMs determines the sign of the Hall voltage. Notably, the electrical switching in the antiferromagnet is made using the same protocol as the one used for ferromagnetic metals. Our observation may well lead to another leap in science and technology for topological magnetism and AF spintronics. This is the work in collaboration with H. Tsai, T. Higo, K. Kondou, T. Nomoto, A. Sakai, A. Kobayashi, T. Nakano, K. Yakushiji, T. Koretsune, M. Suzuki, R. Arita, S. Miwa, Y. Otani, C. Broholm, P. Armitage, H. Chen, A. MacDonald. |
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