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 normal-state 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 symmetry-based 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: Field-angle dependent Majorana gap in a Kitaev spin liquid state of α-RuCl3 Invited Speaker: Takasada Shibauchi An exactly solvable model of two-dimensional honeycome lattice proposed by Kitaev, in which the bond-dependent Ising interactions act as an exchange frustration, leads to a quantum spin liquid (QSL) ground state characterized by Majorana fermions relevant for fault-tolerant topological quantum computations. Recent efforts to search the Kitaev QSL states revealed that in an antiferromagnet α-RuCl3 with layered honeycome structure, the zigzag magnetic order can be suppressed by in-plane magnetic fields, leading to a paramagnetic ground state. In a limited range of this paramagnetic state, thermal Hall transport studies report a half-integer 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 α-RuCl3 under rotated fields in the honeycome plane, which reveal strongly angle-dependent low-energy 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 bulk-edge correspondence in a Kitaev QSL. Moreover, we find the possible emergence of a nematic QSL state with two-fold 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 Sn1-xInxTe (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 Sn1-xInxTe, which is derived from a topological crystalline insulator SnTe, is one such candidate whose topological property has been vigorously debated mainly in bulk crystals. Sn1-xInxTe in a thin-film form compatible with the device fabrication would provide an intriguing platform to explore topological superconductivity. Moreover, thin films of Sn1-xInxTe would also be an useful superconductor to realize interfacial topological superconductivity by fabricating heterostructures with a topological insulator such as (Bi,Sb)2Te3. |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F51.00004: TEM study of aluminum superconductor growth on the in-plane selected area semiconductor nanowire network Svetlana Korneychuk, Frenk Boekhout, Gozde Tutuncuoglu, Kongyi Li, Pavel Aseev, Philippe Caroff-Gaonac'h, Leo Kouwenhoven, Emrah Yucelen Semiconductor nanowires with strong spin-orbit coupling, high mobility and ballistic transport such as InSb and InAs, partially covered in s-wave 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 in-plane selected area nanowire network covered with aluminium. Combination of nanobeam electron diffraction technique with a pixelated detector with high signal-to-noise-ratio allows to obtain the grain orientation in the Al layer with the thickness of 5-10 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 semiconductor-superconductor systems in the presence of magnetic field and spin-orbit coupling have been proposed as building blocks of topological qubits. The existence of these zero modes has been confirmed by zero-bias 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 function-based technique to study electronic transport using the realistic tight-binding models of systems holding Majorana fermions. The method supports multiple orbitals, magnetic field, and spin-orbit coupling, as well as superconductivity in both leads and the system. We also study transport in a T-junction 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 two-dimensional 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 zero-modes (MZMs), building blocks of topologically protected qubits, can be realized in semiconductors with strong spin-orbit interaction coupled to a superconductor. Among the candidate systems, hybrid two-dimensional 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: Shubnikov-de Haas Oscillation in Pb1-xSnxSe topological quantum wells Jiashu Wang, Xinyu Liu, Christian Bunker, Seul-Ki Bac, Maksym Zhukovskyi, Tatyana Orlova, Sergei Rouvimov, Malgorzata Dobrowolska, Jacek Furdyna, Badih A Assaf Pb1-xSnxSe(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 spin-orbit 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 Pb0.92Eu0.08Te/Pb0.7Sn0.3Se/ Pb0.92Eu0.08Te quantum well and characterized the sample by XRD, TEM and magneto-transport measurement. We were able to make single wells with low carrier density and high mobility(>10000cm2/Vs). By properly doping with Bi and gating, Shubnikov-de Haas oscillation were observed. A 2-D 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 Hall-quantized regime of in the quantum limit of TCIs. |
Tuesday, March 16, 2021 1:42PM - 1:54PM Live |
F51.00008: First Angle-Resolved Photoemission Studies of LaNiGa2 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 LaNiGa2 has been observed to be a time reversal symmetry breaking superconductor below 2 Kelvin, large single crystal growths are now available which allow angle-resolved photoemission spectroscopy (ARPES) to probe the electronic structure. We will show the first ARPES studies on LaNiGa2, 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 spin-triplet superconductivity. |
Tuesday, March 16, 2021 1:54PM - 2:06PM Live |
F51.00009: Suppressing Trivial Edge Conductance in Antimonide-based Quantum Spin Hall Materials Minh Nguyen, Andrey A. Kiselev, Diego Carrassco, Mary Chen, Clifford Nguyen, Robert Polski, Stevan Nadj-Perge 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 zero-mode particles. The material system is considered a promising and scalable candidate for topological qubits thanks to (1) the absence of an in-plane magnetic field requirement, (2) its ability to electrically tune into and out of the topological regime and (3) the mature growth and fabrication of 2-dimensional III-V heterostructures. However, it suffers from a non-topological 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 antimonide-based double quantum wells, we are able to reduce the non-topological 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 insulator-based 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 Dirac-like equations at low energies, the spin-momentum 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 high-spin 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 non-centrosymmetric half-heusler 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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