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 Z42: Topological SemimetalsFocus
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Sponsoring Units: DMP Chair: Saurav Islam, Pennsylvania State University Room: Room 318 |
Friday, March 10, 2023 11:30AM - 12:06PM |
Z42.00001: Topological semimetals, topological phase transitions, and candidate materials Invited Speaker: Shuichi Murakami In this talk, we focus on topological semimetals and associated novel properties and discuss candidate materials. The simplest topological semimetal is the Weyl semimetal [1]. The Weyl semimetal often appears as an intermediate phase between different topological phases [2], and we show the band-gap closing is directly related to a change in the topological invariants [1-3]. Such a band-gap closing is accompanied by a polarization jump, and this jump is directly written by a "Weyl dipole" [4]. |
Friday, March 10, 2023 12:06PM - 12:18PM |
Z42.00002: Observing topological edge states in graphene using STM wavefront dislocations Yuval Abulafia, Amit Goft, Nadav Orion, Eric Akkermans We propose a way to systematically measure topological winding numbers in 2D materials with chiral symmetry. We consider the example of graphene with a vacancy, and we prove that it is topological according to the tenfold classification generalised to defects by Teo and Kane. As a result of bulk-edge correspondence, topological edge states appear in the spectrum (zero modes) and are localised around the vacancy. These edge states and their topological winding number are fully characterised by the readout of wavefront dislocations in STM data. Comparison with STM pictures of other (non topological) defects, e.g. adatoms, is discussed. |
Friday, March 10, 2023 12:18PM - 12:30PM Author not Attending |
Z42.00003: Exploring Unconventional Resistivity Scaling in Topological Semimetals for Interconnects Beyond Copper Ching-Tzu Chen, Christian Lavoie, Nicholas A Lanzillo, Utkarsh Bajpai, Oki Gunawan, Asir Intisar Khan, Guy Cohen, Teodor Todorov, John Bruley, Vesna Stanic, Hsin Lin, Ion Garate, Shang-Wei Lien, Yi-Hsin Tu, Gengchiau Liang, Cheng-Yi Huang, Arun Bansil, Sushant Kumar, Ravishankar Sundararaman, Jean Jordan-Sweet, Peter Kerns, Nathan Marchack, Tay-Rong Chang Due to surface and disorder scattering, the polynomial increase in resistivity of conventional metals with shrinking dimensions severely impacts the performance of highly scaled integrated circuits. Here we explore a new class of materials – topological semimetals – as an alternative solution. We demonstrate that, through conduction of the topological surface states, the resistivity in topological semimetals reduces with decreasing feature size in the nanometer scale, even in the presence of defects and grain-boundary scattering. This sharply contrasts the scaling of conventional metals, such as Cu. In this talk, we will present first-principles calculation results of a representative Si-CMOS compatible topological semimetal CoSi, and report experimental evidence for surface-dominated transport in CoSi thin films, showing resistivity below that of the bulk single-crystals. Our proof-of-principle studies demonstrate the potential of topological semimetal interconnects. We will conclude with a set of the guidelines for screening topological semimetals for such applications. |
Friday, March 10, 2023 12:30PM - 12:42PM |
Z42.00004: Bandstructure and optical response of α-Arsenene. Niloufar Dadkhah, Walter R Lambrecht Monolayer group-V structures have been shown to be rich in terms of their topological aspects and how they are protected by symmetries. In particular, density functional theory (DFT) calculations of the α-Sb monolayer show the existence of Dirac points in the band structure due to its non-symmorphic crystal structure. In this talk, we focus on another group-V element, Arsenic, in the monolayer α-form. In particular, we will present its band properties at different levels of theory from DFT to quasi-particle self-consistent GW (QSGW) with and without vertex contributions (ladder diagrams) and with and without spin-orbit coupling (SOC). We also investigate how these properties change as we move from the flat to the puckered α-structure. Moreover, as excitonic effects are important in 2D materials, we study the optical response by means of the Bethe-Salpeter equation (BSE) method. |
Friday, March 10, 2023 12:42PM - 12:54PM |
Z42.00005: Anisotropic positive linear and sub-linear magnetoresistivity in the cubic type-II Dirac metal Pd3In7 Aikaterini Flessa Savvidou, Andrzej Ptok, Girish Sharma, Brian Casas, Judith K Clark, Victoria M Li, Michael Shatruk, Sumanta Tewari, Luis Balicas We report a transport study on Pd3In7 which displays multiple Dirac type-II nodes in its electronic dispersion. Pd3In7 is characterized by low residual resistivities and high mobilities, which are consistent with Dirac-like quasiparticles. For an applied magnetic field μoH having a non-zero component along the electrical current, we find a large, positive, and linear in μoH longitudinal magnetoresistivity (LMR). The sign of the LMR and its linear dependence deviate from the behavior reported for the chiral-anomaly-driven LMR in Weyl semimetals. Interestingly, such anomalous LMR is consistent with predictions for the role of the anomaly in type-II Weyl semimetals. In contrast, the transverse magnetoresistivity (TMR for electric fields E ⊥ μoH) is large and positive, increasing by 103-104 % as a function of μoH while following an anomalous, angle-dependent power law ρxx ∼ (μoH)β with β(θ) ≤ 1. The order of magnitude of the TMR, and its anomalous power-law, is explained in terms of uncompensated electron and hole-like Fermi surfaces characterized by anisotropic carrier scattering likely resulting from the absence of Lorentz invariance. |
Friday, March 10, 2023 12:54PM - 1:06PM |
Z42.00006: Electronic Structure of Quasi-1D Topological Nodal-line Semimetals Asish K Kundu, Renu Choudhary, Santanu Pakhira, Tufan Roy, Turgut Yilmaz, Elio Vescovo, Masafumi Shirai, David C Johnston, Abhay N Pasupathy, Tonica Valla Nodal line semimetals (NLSMs) are symmetry-protected topological materials with Dirac/Weyl-type band crossings that extend into loops or lines in reciprocal space. These materials often show novel transport properties, including highly-anisotropic magnetoresistance, quantum oscillations, and non-zero Berry curvatures [1-2]. Using angle-resolved photoemission spectroscopy (ARPES) and density-functional-theory calculations, we have shown that quasi-1D structure tellurides TaXTe5 (X = Ni, Pt) are NLSMs, hosting Dirac-like surface states and nodal lines with quasi-2D electronic structures. These Dirac-like states exhibit complex dichroism in ARPES. We have also shown that when electrons are doped into these systems, the Fermi surfaces change dramatically and flat-band-like electronic states appear near the Fermi energy (EF). The energy position of the flat-band is also highly tunable by controlling the doping. Flat-bands around EF may enhance electronic correlations that can lead to novel transport properties. |
Friday, March 10, 2023 1:06PM - 1:18PM |
Z42.00007: Surface state hybridization and tunable band inversion in cadmium arsenide thin films Alexander C Lygo, Binghao Guo, Arman Rashidi, Susanne Stemmer Thin films of the three-dimensional Dirac semimetal cadmium arsenide (Cd3As2) provide a route for realizing new topological phases via band structure engineering techniques available in thin film growth. Recently, magnetotransport experiments showed evidence of surface state hybridization in very thin films of (001) Cd3As2, opening the possibility of realizing a two-dimensional topological insulator (2D TI) state. In this talk we discuss the evolution of the surface states of (001) Cd3As2 films as the thickness is reduced to the regime where hybridization of the surface states occurs. Utilizing magnetotransport measurements performed on gated Hall bar structures, we observe a Landau level spectrum and quantum Hall effect that is in excellent agreement with that predicted for a 2D TI produced via surface state hybridization. Further, we show that a small reduction in film thickness results in a quantum phase transition from a 2D TI state to a trivial insulating state, consistent with theoretical predictions. Our results demonstrate that thin films of Cd3As2 are a rich and tunable platform for exploring the novel properties of quantum materials. |
Friday, March 10, 2023 1:18PM - 1:30PM |
Z42.00008: Less is more: Vacancy-engineered interacting nodal-line semimetals Mariana Malard Sales Andrade We show that lattice engineering with certain periodic distributions of vacancies yields a novel type of nodal-line semimetal which possess symmetry-enforced nodal lines, which are immune to arbitrarily large symmetry-preserving perturbations, and unusually robust accidental nodal lines. Both types of nodal lines arise from the structural features of the proposed vacancy-engineered lattices, as demonstrated using a minimal effective model and verified by first-principles calculations of vacancy-engineered graphene and borophene sheets. The effect of electron-electron (e-e) interaction in vacancy-engineered graphene is addressed by quantum Monte Carlo simulations. Former studies of the pristine honeycomb lattice have demonstrated the occurrence of a quantum phase transition from a metallic to an insulating antiferromagnetic phase at a critical strength of the e-e interaction. We investigate if a long-range magnetic order exists in vacancy-engineered graphene and, if so, what type of magnetic order and the relation between the existence of nodal lines in the single-particle spectrum and the onset of the magnetic order in the interacting case. |
Friday, March 10, 2023 1:30PM - 1:42PM |
Z42.00009: Strong Room-Temperature Bulk Nonlinear Hall Effect in a Spin-Valley Locked Dirac Material Lujin Min, Hengxin Tan, Zhijian Xie, Leixin Miao, Ruoxi Zhang, Seng Huat Lee, Venkatraman Gopalan, Chaoxing Liu, Nasim Alem, Binghai Yan, Zhiqiang Mao Nonlinear Hall effect (NLHE) represents a new type of Hall effect characterized by alternating current (a.c.) driven second-harmonic and rectified Hall voltage response under time-reversal symmetry and has wide application prospects such as THz detection. Practical device applications require room temperature (RT) NLHE with the ability to produce large photocurrent. However, among the current materials showing NLHE, the observed NLHE is primarily a low-temperature phenomenon. TaIrTe4 is only the material showing NLHE at RT, but its NLHE only stems from surface layers. Bulk RT NLHE is highly desired due to its ability to generate large photocurrent but has not been reported yet. In this talk, we show the bulk spin-valley locked state in BaMnSb2 can generate a strong bulk NLHE at RT. In the microscale devices, we observed not only a.c.-driven second-harmonic and rectification Hall responses but also a NLH response driven by d.c. Moreover, our measurements also find the NLHE of BaMnSb2 shows a maximum near RT, which agrees well with the calculated energy dependence of the Berry curvature dipole, indicating the Dirac state origin of the observed NLHE. Additionally, we also demonstrated RT wireless microwave detection and frequency doubling based on the observed NLHE. These findings broaden the coupled spin and valley physics from 2D systems into a 3D system and lay a foundation for exploring bulk NLHE’s applications at RT. |
Friday, March 10, 2023 1:42PM - 1:54PM |
Z42.00010: Growth of bulk like epitaxial films of Weyl semimetal TaAs on GaAs (001) Jocienne N Nelson, Anthony Rice, Ian Leahy, Rafal Kurleto, John Mangum, Amanda Shackelford, Mark van Schilfgaarde, Megan Holtz, Dan S Dessau, Kirstin M Alberi Three dimensional topological semimetals (TSMs) exhibit extraordinary properties such as extremely high mobility, conductivity and magnetoresistance stemming from their protected bandstructures. They are now emerging as excellent candidates for a wide variety of applications including spintronics, thermoelectrics, and catalysts. While there has been a great deal of success studying novel bulk single crystal TSMs, they are not suitable for device applications. Thus, there is a need to develop thin film TSMs compatible with semiconductor manufacturing to accelerate the adoption of TSMs into devices. We report epitaxial growth of thick bulk-like films of Weyl semimetal TaAs on GaAs(001) substrates using molecular beam epitaxy. TaAs has been widely studied in bulk crystal form but only synthesized in thin films as ultrathin materials (10-20 nm), in which electron transport is dominated by surface states. In this presentation we discuss growth strategies to realize thick (100-300 nm) single crystal films and eliminate secondary phases. We study the electronic structure using a combination of magnetotransport and angle resolved photoemission spectroscopy. We will also discuss the impact of epitaxial growth on intrinsic doping and magnetoresistance. |
Friday, March 10, 2023 1:54PM - 2:06PM |
Z42.00011: Thermomechanical Nanomolding of Topological Materials Quynh Sam, Mehrdad T Kiani, Gangtae Jin, Betul Pamuk, James L Hart, Hyeuk Jin Han, Judy J Cha Topological nanomaterials have novel symmetry-protected electronic states that are advantageous for applications such as microelectronics and quantum computing. Fabrication of topological nanomaterials is hindered by the lack of high throughput synthesis methods that enable tight control of phase and morphology. Here, we present the use of thermomechanical nanomolding (TMNM) to fabricate nanowires of topological materials. TMNM is a materials agnostic, scalable fabrication process where a bulk feedstock is pressed through a nanoporous mold at elevated temperatures and pressures to form defect-free, single crystal nanowires. |
Friday, March 10, 2023 2:06PM - 2:18PM |
Z42.00012: Quantized optical Hall current in topological nodal-line semimetal Po-Hsin Shih, Thi-Nga Do, Godfrey Gumbs, Danhong Huang, Hsin Lin, Tay-Rong Chang Photocurrent acts as one of measurable responses of material to light, which has proved itself to be crucial for sensing and energy harvesting. Topological semimetals with gapless energy dispersion and abundant topological surface and bulk states exhibit exotic photocurrent responses, such as novel quantized circular photogalvanic effect observed in Weyl semimetals. Here we find that for a topological nodal-line semimetal (NLSM) with nodal ring bulk states and drumhead surface states (DSS), a significant photocurrent can be produced by an electromagnetic (EM) wave by means of the optical Hall effect. The optical Hall current is enabled by electron transfer between Landau levels (LLs) and triggered by both the electric field and magnetic field components of an EM wave. This optical Hall current is physically connected to an unusually large quantum-Hall conductivity of the zeroth LLs resulting from quantized DSS. These LLs are found to be highly degenerate due to the unique band-folding effect associated with magnetic-field-induced expansion of a unit cell. Furthermore, we observe that the optical Hall current induced solely by an in-plane linearly-polarized EM wave becomes a quantized entity which allows for possible direct measurement of the DSS density in a topological NLSM. This work paves a way toward designing high-magnetic-field-sensitivity detection devices for industrial and space applications, such as the development of self-detection of current-surge-induced overheating in electronic devices and accurate Earth's magnetic-anomaly maps for guiding a self-navigating drone or an aircraft. |
Friday, March 10, 2023 2:18PM - 2:30PM |
Z42.00013: Synthesis and characterization of Cd3As2 heterostructures as a route to broken time reversal symmetry in a Dirac semimetal Emma K Steinebronn, Run Xiao, Saurav Islam, Wilson J Yanez, Supriya Ghosh, Yongxi Ou, Juan Chamorro, Andre Mkhoyan, Tyrel M McQueen, Yi Li, Nitin Samarth Thin films of Cd3As2 have attracted significant interest in recent years for studying the effects of quantum confinement and strain on a canonical Dirac semimetal. Such epitaxially grown thin films also provide an opportunity to explore proximity effects that break time-reversal symmetry. Magnetically-doped III-V semiconductors are attractive in this context because they serve as excellent ferromagnetic substrates for the growth by molecular beam epitaxy (MBE) of Cd3As2 films of reasonable interfacial, structural, and electronic quality. To this end, we report on the MBE growth of Cd3As2 thin films on (In,Mn)As (001) which is a well-established ferromagnetic semiconductor with perpendicular magnetic anisotropy. A key challenge is to engineer heterostructures with sharp interfaces and with electrical transport dominated by the Cd3As2 layer. We characterize the structural characteristics of these heterostructures using x-ray diffraction, atomic force microscopy, and high-resolution transmission electron microscopy. We also use Hall effect measurements to search for evidence of proximity-induced magnetism in the Cd3As2 layer. Finally, we will report on measurements of angle-resolved photoemission spectroscopy above and below the Curie temperature of the (In,Mn)As layer. |
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