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 F51: Topological Materials: Majoranas, Superconductivity and Thin filmsFocus Live

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Sponsoring Units: DMP Chair: Xiong Yao, Rutgers University, New Brunswick 
Tuesday, March 16, 2021 11:30AM  12:06PM Live 
F51.00001: Symmetry indicators for topological superconductors Invited Speaker: Hoi Chun Po A useful guiding principle for the search of topological superconductors is to relate the topological invariants to the behavior of the pairing order parameter on the normalstate Fermi surfaces. In this talk, we will discuss how this paradigm can be integrated with the notion of symmetry indicators [1]. The theory of symmetry indicators utilizes symmetry data of band structures to detect nontrivial topology, and it has enabled efficient surveys of topological materials candidates [2]. We will highlight the conceptual similarities and differences between such symmetrybased diagnostics for insulators and semimetals as compared to that for superconductors [3], and also address how the diagnosis can be integrated with ab initio calculations to predict the physical properties of unconventional superconductors [4]. 
Tuesday, March 16, 2021 12:06PM  12:42PM Live 
F51.00002: Fieldangle dependent Majorana gap in a Kitaev spin liquid state of αRuCl_{3} Invited Speaker: Takasada Shibauchi An exactly solvable model of twodimensional honeycome lattice proposed by Kitaev, in which the bonddependent Ising interactions act as an exchange frustration, leads to a quantum spin liquid (QSL) ground state characterized by Majorana fermions relevant for faulttolerant topological quantum computations. Recent efforts to search the Kitaev QSL states revealed that in an antiferromagnet αRuCl_{3} with layered honeycome structure, the zigzag magnetic order can be suppressed by inplane magnetic fields, leading to a paramagnetic ground state. In a limited range of this paramagnetic state, thermal Hall transport studies report a halfinteger quantized plateau behavior [1,2], a signature of Majorana fermions whose degrees of freedom are half of electrons. However, the bulk nature of this state is still elusive. Here we report on detailed heat capacity measurements of αRuCl_{3} under rotated fields in the honeycome plane, which reveal strongly angledependent lowenergy excitations in the bulk. The excitation gap has a sextuple node structure, and the gap amplitude increases with field, exactly as expected for itinerant Majorana fermions in the Kitaev model [3]. Our thermodynamic results are fully linked with the transport quantization properties, providing the first demonstration of the bulkedge correspondence in a Kitaev QSL. Moreover, we find the possible emergence of a nematic QSL state with twofold rotational symmetry at high fields, which may be relevant to the vanishing of quantum thermal Hall effect. 
Tuesday, March 16, 2021 12:42PM  12:54PM Live 
F51.00003: Molecular beam epitaxy of superconducting Sn_{1x}In_{x}Te (0 ≤ x ≤ 0.66) thin films Makoto Masuko, Ryutaro Yoshimi, Atsushi Tsukazaki, Minoru Kawamura, Kei Takahashi, Masashi Kawasaki, Yoshinori Tokura Topological superconductivity has attracted increasing interest these days. A superconductor Sn_{1x}In_{x}Te, which is derived from a topological crystalline insulator SnTe, is one such candidate whose topological property has been vigorously debated mainly in bulk crystals. Sn_{1x}In_{x}Te in a thinfilm form compatible with the device fabrication would provide an intriguing platform to explore topological superconductivity. Moreover, thin films of Sn_{1x}In_{x}Te would also be an useful superconductor to realize interfacial topological superconductivity by fabricating heterostructures with a topological insulator such as (Bi,Sb)_{2}Te_{3}. 
Tuesday, March 16, 2021 12:54PM  1:06PM Live 
F51.00004: TEM study of aluminum superconductor growth on the inplane selected area semiconductor nanowire network Svetlana Korneychuk, Frenk Boekhout, Gozde Tutuncuoglu, Kongyi Li, Pavel Aseev, Philippe CaroffGaonac'h, Leo Kouwenhoven, Emrah Yucelen Semiconductor nanowires with strong spinorbit coupling, high mobility and ballistic transport such as InSb and InAs, partially covered in swave superconductor are one of the actively developing platforms for Majorana zero modes, building blocks for topologically protected quantum computing. The semiconductor/superconductor interface is the most crucial part of the nanowire as Majoranas should emerge there. Aluminium is one of the most promising materials for a superconductor, providing a better quality interface than, for instance, niobium titanium nitride. Here, we demonstrate how transmission electron microscopy (TEM) can assess the quality of the Al superconductor layer, in particular the orientation and size distribution of grains, interface quality and grain boundaries. This study is carried out on the inplane selected area nanowire network covered with aluminium. Combination of nanobeam electron diffraction technique with a pixelated detector with high signaltonoiseratio allows to obtain the grain orientation in the Al layer with the thickness of 510 nm. 
Tuesday, March 16, 2021 1:06PM  1:18PM Not Participating 
F51.00005: Electronic transport studies of architectures supporting Majorana fermions Sayandip Dhara, Eduardo R Mucciolo Majorana zero modes that exist in hybrid semiconductorsuperconductor systems in the presence of magnetic field and spinorbit coupling have been proposed as building blocks of topological qubits. The existence of these zero modes has been confirmed by zerobias conductance peaks on electronic transport measurements on these systems. The next goal is to realistically observe the fusion and braiding of these Majorana zero modes and look for transport characteristics of these phenomena. Here, we develop a recursive Green’s functionbased technique to study electronic transport using the realistic tightbinding models of systems holding Majorana fermions. The method supports multiple orbitals, magnetic field, and spinorbit coupling, as well as superconductivity in both leads and the system. We also study transport in a Tjunction with multiple leads to understand the signatures of the exchange of the Majorana zero modes that reside in either the same or different topological regions. 
Tuesday, March 16, 2021 1:18PM  1:30PM Live 
F51.00006: InSbAs twodimensional electron gases as a platform for topological superconductivity Christian Moehle, Chung Ting Ke, Candice Thomas, Di Xiao, Mario Lodari, Vincent van de Kerkhof, Ruben Termaat, Saurabh Karwal, Sara Metti, Charles Guinn, Raymond Kallaher, Geoffrey C. Gardner, Giordano Scappucci, Michael Manfra, Srijit Goswami Majorana zeromodes (MZMs), building blocks of topologically protected qubits, can be realized in semiconductors with strong spinorbit interaction coupled to a superconductor. Among the candidate systems, hybrid twodimensional electron gases (2DEGs) are of particular interest due to their inherent design flexibility and scalability. 
Tuesday, March 16, 2021 1:30PM  1:42PM Live 
F51.00007: Shubnikovde Haas Oscillation in Pb_{1x}Sn_{x}Se topological quantum wells Jiashu Wang, Xinyu Liu, Christian Bunker, SeulKi Bac, Maksym Zhukovskyi, Tatyana Orlova, Sergei Rouvimov, Malgorzata Dobrowolska, Jacek Furdyna, Badih A Assaf Pb_{1x}Sn_{x}Se(0.16<x<0.4) is a semiconductor with narrow band gap and can transit from trivial to topological crystalline insulator (TCI) as Sn concentration increases. It is a valley degenerate system with strong spinorbit coupling, providing a platform to study exotic quantum Hall phenomenon. However, such effect can only be achieved on high quality quantum wells, which have not been well studied yet. Here we investigated the MBE growth of Pb_{0.92}Eu_{0.08}Te/Pb_{0.7}Sn_{0.3}Se/ Pb_{0.92}Eu_{0.08}Te quantum well and characterized the sample by XRD, TEM and magnetotransport measurement. We were able to make single wells with low carrier density and high mobility(>10000cm^{2}/Vs). By properly doping with Bi and gating, Shubnikovde Haas oscillation were observed. A 2D density and effective mass are calculated from the oscillation correlate well with Hall measurements. The oscillations also agree with what is expected for the Landau levels extracted from a k.p quantum well model allows us to estimate that B=20T is required to reach the quantum limit. Our work has achieves needed progress for future studies of the unconventional Hallquantized regime of in the quantum limit of TCIs. 
Tuesday, March 16, 2021 1:42PM  1:54PM Live 
F51.00008: First AngleResolved Photoemission Studies of LaNiGa_{2} Matthew Staab, Jackson Badger, Yundi Quan, Antonio Rossi, Kasey Devlin, Kelly Neubauer, Chris Perez, Jim Fettinger, Peter Klavins, Susan Kauzlarich, Dai Aoki, Warren Pickett, Valentin Taufour, Inna Vishik LaNiGa_{2} has been observed to be a time reversal symmetry breaking superconductor below 2 Kelvin, large single crystal growths are now available which allow angleresolved photoemission spectroscopy (ARPES) to probe the electronic structure. We will show the first ARPES studies on LaNiGa_{2}, showing 3D band dispersion and fermiology consistent with first principles calculations. ARPES data provides evidence for band degeneracies at the Fermi surface, a predicted mechanism for the observed spintriplet superconductivity. 
Tuesday, March 16, 2021 1:54PM  2:06PM Live 
F51.00009: Suppressing Trivial Edge Conductance in Antimonidebased Quantum Spin Hall Materials Minh Nguyen, Andrey A. Kiselev, Diego Carrassco, Mary Chen, Clifford Nguyen, Robert Polski, Stevan NadjPerge InAs/GaSb double quantum wells are predicted to possess a quantum spin Hall phase with insulating bulk and conducting helical edge states, which can host Majorana zeromode particles. The material system is considered a promising and scalable candidate for topological qubits thanks to (1) the absence of an inplane magnetic field requirement, (2) its ability to electrically tune into and out of the topological regime and (3) the mature growth and fabrication of 2dimensional IIIV heterostructures. However, it suffers from a nontopological parasitic conductance that could hamper the desired topological properties of the helical edge states. In this talk, we will discuss our recent results in solving this technological road block for the material system. By studying different variants of antimonidebased double quantum wells, we are able to reduce the nontopological edge resistance by more than 1 order of magnitude, and significantly improve the bulk resistance in the topological regime. 
Tuesday, March 16, 2021 2:06PM  2:18PM Live 
F51.00010: Boundary conditions and bound states in lateral topological insulatorbased junctions Eklavya Thareja, Ilya Vekhter Topological insulators have been part of many proposals for applications of topological phases of matter. Many of these involve forming interfaces and junctions with other materials. Recent studies have highlighted that, while both surface and interface states satisfy Diraclike equations at low energies, the spinmomentum locking may differ between the two. We derive the topological boundary conditions for the wavefunction at a lateral junction between the two, connect it with the detailed structure of both potential and magnetic scattering at the junction, and discuss the existence and the properties of the states localized near such junctions. 
Tuesday, March 16, 2021 2:18PM  2:30PM Live 
F51.00011: Effect of disorder on highspin topological superconductor YPtBi Prathum Saraf, Rahul Sharma, Connor Roncaioli, Hyunsoo Kim, Johnpierre Paglione YPtBi has been a candidate to study the interplay between superconductivity and topological band structure. With a noncentrosymmetric halfheusler structure it has a topological band structure and an extremely low carrier density. Along with that it also hosts a superconducting transition at 0.8K with a high spin (j=3/2) pairing state and a nodal order parameter. In order to gain some further insight into the nature of the superconducting state, we report on a variety of measurements to understand the effect of disorder on the material and probe the pair breaking effect as a function of disorder on the superconducting state. 
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