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 2MWS_{2} Invited Speaker: Wei Li A possible topological superconductor 2MWS_{2} has been discovered and its superconducting transition temperature is ~ 8.8 K. By using lowtemperature 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 Carolide GennesMatricon bound states inside the vortexcore, 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 gaugeinvariant 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 [24] 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 ironbased superconductor FeTe1xSex has attracted considerable attention as a candidate 
Monday, March 2, 2020 3:30PM  3:42PM 
D60.00004: Molecular Beam Epitaxy Growth of Superconducting Sn_{1x}In_{x}Te (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, alltelluride based heterostructures consisting of TI (Bi,Sb)_{2}Te_{3} and Tebased superconductor (SC) may be a promising candidate. As the first step toward TI/SC heterostructures, epitaxial growth of Tebased SC is required. 
Monday, March 2, 2020 3:42PM  3:54PM 
D60.00005: Proximityinduced 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 Z_{2} topological insulators (TIs). While superconducting proximity effect has been widely used to induce superconductivity in Z_{2} 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 lowtemperature 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 twodimensional C_{n}−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 C_{6} symmetric 2D topological crystalline insulators (TCIs). We thoroughly investigate the fractional charge on disclinations in C_{n }symmetric TCIs, with or without timereversal symmetry, and including spinless and spin1/2 cases. We find the disclination charge is fractionalized in units of e/n for C_{n} symmetric TCIs; and for spin1/2 TCIs, with additional timereversal 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 nonzero 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 C_{n}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. Twodimensional (2D) topological crystalline insulators (TCI) are ideal materials for achieving this switch, as their edge states can be turned on/off by applying a symmetrybreaking 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 tightbinding models, we show that the edge states of TCI bismuthene can be stabilized on some substrates (e.g. hBN 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 PbSnInTe 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 Pbsystem ( PbSnInTe) 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 T_{c=}5K_{.} 
Monday, March 2, 2020 4:30PM  4:42PM 
D60.00009: Superconducting proximity effect in InAsSb surface quantum wells with insitu 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 InAs_{0.5}Sb_{0.5} 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 InAs_{0.5}Sb_{0.5} supports stronger spinorbit coupling and a larger gfactor. Through structural and transport characterization we observe highquality interfaces and strong spinorbit coupling. We fabricate Josephson junctions based on InAs_{0.5}Sb_{0.5} quantum wells and observe a strong proximity effect. These junctions exhibit products of normal resistance and critical current, I_{c}R_{N} = 270μV, and excess current, I_{ex}R_{N} = 200μV, at contact separations of 500nm. Both of these quantities demonstrate a robust and longrange proximity effect with highlytransparent 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, TayRong Chang, Rongying Jin PdTe is a superconductor with T_{c} ~ 4.5 K. We have investigated its normalstate electronic properties via both first principles calculations and magnetic torque measurements by applying magnetic field up to 35 Tesla. Detailed analysis of the deHaas van Alphen (dHvA) oscillations allows us to identify four frequencies: F_{α} = 64 T, F_{β} = 658 T, F_{γ} = 1155 T, and F_{η} = 1867 T. Using the LifshitzKosevich equation to fit the experimental data, the effective masses are obtained with m*_{α }= 0.305m_{0}, m*_{β }= 0.288m_{0}, m*_{γ }= 0.415m_{0}, and m*_{η }= 0.451m_{0} (m_{0} is the free electron mass). By constructing the Landau fan diagram for each band, we extract the Berry phase, which is nontrivial 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:
firstprinciples study Ivan Naumov, Pratibha Dev Recent studies have shown that bismuth is a crystalline topological insulator and, additionally, hosts two different secondorder band topologies that are protected by twofold and the threefold rotational symmetries [1,2]. These secondorder topologies manifest themselves in onedimensional hinge states in samples whose shape preserve the corresponding rotational symmetry [1,2]. Using firstprinciples calculations we show that the hinge states can be significantly tuned by H and N adsorption. We discuss the changes in their dispersion curves, realspace 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, QingRui Wang, Zhengcheng Gu Abelian ChernSimons theory, labeled by the socalled $K$ 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 ChernSimons 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 OsX_{2} (X= Se, Te) Crystals Yuefeng Yin, Michael Fuhrer, Nikhil Medhekar The development of nextgeneration spinbased 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 OsX_{2} (X = Se, Te) crystals using first principles calculations and Wannier tightbinding models. The surface spin textures of topologically nontrivial OsX_{2} features a transition from inplane to outofplane 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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