Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session D60: Topological Materials: Topological Superconductors and Majorana StatesFocus
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Sponsoring Units: DMP Chair: Norman Armitage, Johns Hopkins University Room: Mile High Ballroom 4A |
Monday, March 2, 2020 2:30PM - 3:06PM |
D60.00001: Evidence of anisotropic Majorana bound states in 2M-WS2 Invited Speaker: Wei Li A possible topological superconductor 2M-WS2 has been discovered and its superconducting transition temperature is ~ 8.8 K. By using low-temperature scanning tunneling microscopy, we have made direct observation of a clean Majorana zero mode in this transition metal dichalcogenide. The observed Majorana zero mode well separates in energy from the Caroli-de Gennes-Matricon bound states inside the vortex-core, therefore providing a good platform for the future quantum computing. |
Monday, March 2, 2020 3:06PM - 3:18PM |
D60.00002: Applications of a Novel Quantum Interband Index in Condensed Matter: Topological Insulators, Optical Selection Rules, and Beyond Tharindu Warnakulasooriya Fernando, Ting Cao, Congjun Wu The physical significance of a novel gauge-invariant interband index T proposed in [1] is not immediately clear in condensed matter systems. In this talk, we present numerical calculations of the index T in various systems. Calculations of T in loops around valleys of the Haldane model for the anomalous quantum Hall effect give distinct integer numbers with behavior partly reminiscent of different types of Chern numbers (such as spin or valley). For loops containing more/less than 1 Dirac point, our calculations reveal perplexing results including a link to the sign of local Berry curvature. We further connect this index to recently discovered optical selection rules [2-4] and demonstrate other physical effects related to T. |
Monday, March 2, 2020 3:18PM - 3:30PM |
D60.00003: Bulk superconductivity in FeTe1−xSex via physicochemical pumping of excess iron Lianyang Dong, He Zhao, Ilija Zeljkovic, Stephen Wilson, John W Harter The iron-based superconductor FeTe1-xSex has attracted considerable attention as a candidate |
Monday, March 2, 2020 3:30PM - 3:42PM |
D60.00004: Molecular Beam Epitaxy Growth of Superconducting Sn1-xInxTe (0 ≤ x ≤ 0.67) Thin Films Makoto Masuko, Ryutaro Yoshimi, Atsushi Tsukazaki, Minoru Kawamura, Kei Takahashi, Masashi Kawasaki, Yoshinori Tokura Topological superconductivity has attracted increasing interest for not only its novel properties but also the possible application to quantum computing. One way to realize topological superconductivity is to induce superconducting gap in the surface states of topological insulators (TIs) by the proximity effect. To maximize the superconducting proximity effect, all-telluride based heterostructures consisting of TI (Bi,Sb)2Te3 and Te-based superconductor (SC) may be a promising candidate. As the first step toward TI/SC heterostructures, epitaxial growth of Te-based SC is required. |
Monday, March 2, 2020 3:42PM - 3:54PM |
D60.00005: Proximity-induced superconductivity in SnTe thin films Bryan Rachmilowitz, He Zhao, Hong Li, Alexander LaFleur, John Schneeloch, Ruidan Zhong, Genda Gu, Ilija Zeljkovic Superconducting topological crystalline insulators (TCIs) are theorized to host new types of topologically protected surface states distinct from those at the surface of superconducting Z2 topological insulators (TIs). While superconducting proximity effect has been widely used to induce superconductivity in Z2 TIs, the efforts to induce superconductivity in TCIs have been hindered by growth difficulties. Here we report the synthesis of heterostructures of a prototypical TCI SnTe(111) and high temperature superconductor Fe(Te,Se) using molecular beam epitaxy. Utilizing low-temperature scanning tunneling microscopy and spectroscopy as function of temperature and magnetic field, we show strong evidence of induced superconductivity at the surface of SnTe. Our work provides a new platform for studying emergent phenomena in superconducting TCIs. |
Monday, March 2, 2020 3:54PM - 4:06PM |
D60.00006: Fractional disclination charge in two-dimensional Cn−symmetric topological crystalline insulators Tianhe Li, Penghao Zhu, Wladimir A Benalcazar, Taylor L Hughes Robust fractional charge localized at disclination defects has been recently found as a topological response in C6 symmetric 2D topological crystalline insulators (TCIs). We thoroughly investigate the fractional charge on disclinations in Cn symmetric TCIs, with or without time-reversal symmetry, and including spinless and spin-1/2 cases. We find the disclination charge is fractionalized in units of e/n for Cn symmetric TCIs; and for spin-1/2 TCIs, with additional time-reversal symmetry, the disclination charge is fractionalized in units of 2e/n. Utilizing band representation theory, we construct topological indices of the fractional disclination charge for all 2D TCIs that admit a (generalized) Wannier representation. Moreover, we use an algebraic technique to generalize the indices for TCIs with non-zero Chern numbers, where a (generalized) Wannier representation is not applicable. Our results provide a quantitative and intuitive understanding of fractional charge at defects for 2D Cn-symmetric TCIs. |
Monday, March 2, 2020 4:06PM - 4:18PM |
D60.00007: Tuning the Edge States of Topological Crystalline Insulator Bismuthene via Substrate Effects Chutian Wang, Yuefeng Yin, Michael Fuhrer, Nikhil Medhekar One of the key challenges in design of devices bases on topological materials is to conveniently turn the surface and edge states on and off. Two-dimensional (2D) topological crystalline insulators (TCI) are ideal materials for achieving this switch, as their edge states can be turned on/off by applying a symmetry-breaking field. However, it remains unresolved how 2D TCI phases can be integrated in experimental devices due to the difficulty in synthesis and the complex interactions between TCI and underlying substrates. In this theoretical study based on first principles calculations and Wannier tight-binding models, we show that the edge states of TCI bismuthene can be stabilized on some substrates (e.g. h-BN and SiC) when the stacking pattern does not break mirror symmetry. We can achieve fine tuning of the edge states of bismuthene by applying strain or an external electric field. This research provides guidelines for selection of appropriate substrates for the experimental realization of topological edge states and the methodology to tune the edge states in 2D TCIs. |
Monday, March 2, 2020 4:18PM - 4:30PM |
D60.00008: Searching for ideal topological crystalline insulators and topological superconductors in Pb-Sn-In-Te system Genda Gu, Ruidan Zhong, Yangmu Li, Qiang Li, Tonica Valla, John Tranquada The discovery of 3D topological insulator materials and topological superconductor open up a new research field in the condensed matter physics. In order to search for the topological superconductor, we have grown a large number of the single crystals of Pb-system ( Pb-Sn-In-Te) topological crystalline insulator and their topological superconductor . We have measured the physical properties on these single crystals by various techniques. We have studied the effect of crystal growth condition, impurity and composition on the bulk electrical conductivity of these single crystals. We try to find out which composition and crystal growth condition is the best for the ideal topological insulator, topological crystalline insulator and topological superconductor. We have got the bulk topological superconductor with Tc=5K. |
Monday, March 2, 2020 4:30PM - 4:42PM |
D60.00009: Superconducting proximity effect in InAsSb surface quantum wells with in-situ Al contacts William Schiela, William Mayer, Joseph Yuan, Mehdi Hatefipour, Wendy L Sarney, Stefan P Svensson, Asher Leff, Tiago De Campos, Kaushini S Wickramasinghe, Matthieu Dartiailh, Igor Zutic, Javad Shabani We demonstrate a robust superconducting proximity effect in InAs0.5Sb0.5 quantum wells grown with epitaxial Al contacts, which has important implications for mesoscopic and topological superconductivity. Unlike more commonly studied InAs and InSb semiconductors, bulk InAs0.5Sb0.5 supports stronger spin-orbit coupling and a larger g-factor. Through structural and transport characterization we observe high-quality interfaces and strong spin-orbit coupling. We fabricate Josephson junctions based on InAs0.5Sb0.5 quantum wells and observe a strong proximity effect. These junctions exhibit products of normal resistance and critical current, IcRN = 270μV, and excess current, IexRN = 200μV, at contact separations of 500nm. Both of these quantities demonstrate a robust and long-range proximity effect with highly-transparent contacts. |
Monday, March 2, 2020 4:42PM - 4:54PM |
D60.00010: Topological Properties of Superconducting PdTe Ramakanta Chapai, Peram Sreenivasa Reddy, Lingyi Xing, David E Graf, Amar B. Karki, Weiwei Xie, John Ditusa, Tay-Rong Chang, Rongying Jin PdTe is a superconductor with Tc ~ 4.5 K. We have investigated its normal-state electronic properties via both first principles calculations and magnetic torque measurements by applying magnetic field up to 35 Tesla. Detailed analysis of the de-Haas van Alphen (dHvA) oscillations allows us to identify four frequencies: Fα = 64 T, Fβ = 658 T, Fγ = 1155 T, and Fη = 1867 T. Using the Lifshitz-Kosevich equation to fit the experimental data, the effective masses are obtained with m*α = 0.305m0, m*β = 0.288m0, m*γ = 0.415m0, and m*η = 0.451m0 (m0 is the free electron mass). By constructing the Landau fan diagram for each band, we extract the Berry phase, which is non-trivial for the α and γ bands. These experimental findings are consistent with the calculated results. This suggests that PdTe is a topological superconductor. |
Monday, March 2, 2020 4:54PM - 5:06PM |
D60.00011: Tuning topological hinge states of Bi by edge adsorption:
first-principles study Ivan Naumov, Pratibha Dev Recent studies have shown that bismuth is a crystalline topological insulator and, additionally, hosts two different second-order band topologies that are protected by twofold and the threefold rotational symmetries [1,2]. These second-order topologies manifest themselves in one-dimensional hinge states in samples whose shape preserve the corresponding rotational symmetry [1,2]. Using first-principles calculations we show that the hinge states can be significantly tuned by H and N adsorption. We discuss the changes in their dispersion curves, real-space charge distributions and spin texture. Our findings may have practical applications in future electronic devices. |
Monday, March 2, 2020 5:06PM - 5:18PM |
D60.00012: The edge theories of 2D fermionic symmetry protected topological phases Shangqiang Ning, Chenjie Wang, Qing-Rui Wang, Zhengcheng Gu Abelian Chern-Simons theory, labeled by the so-called $K$ matrices, have been quite successful in characterizing and classifying Abelian fractional quantum hall effect(FQHE) as well as symmetry protected topological(SPT) phases, especially for bosonic SPT phases. However, there are still some puzzles in dealing with fermionic SPT phases. In this paper, we utilize the Abelian Chern-Simons theory to study the fermionic SPT phases protected by Abelian total symmetry $G_f$ that is a central extension of bosonic symmetry $G_b$ by fermion parity symmetry $Z_2^f$. |
Monday, March 2, 2020 5:18PM - 5:30PM |
D60.00013: Selective Control of Surface Spin Current in Topological Pyrite OsX2 (X= Se, Te) Crystals Yuefeng Yin, Michael Fuhrer, Nikhil Medhekar The development of next-generation spin-based nanoelectronic devices requires effective control and detection of spin polarization. Recently topological materials have shown promising potential in this field due to their unique spin textures. Here we report the discovery of highly anisotropic surface spin textures in the (001) surfaces of topological pyrite OsX2 (X = Se, Te) crystals using first principles calculations and Wannier tight-binding models. The surface spin textures of topologically nontrivial OsX2 features a transition from in-plane to out-of-plane spin polarization in the momentum space and are protected by local crystalline symmetries. The energy screening of bulk bands leads to selective filtering of the magnitude and orientations of the surface spin polarization. These results provide new physical insights for manipulating spin degree of freedom in spin logic devices and could inspire new strategies of search nonmagnetic materials hosting exotic spin properties. |
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