Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session J60: Josephson Junctions with Topological Insulator Weak LinksFocus
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Sponsoring Units: DMP Chair: David Cobden, University of Washington Room: Mile High Ballroom 4A |
Tuesday, March 3, 2020 2:30PM - 3:06PM |
J60.00001: Josephson Junctions Using Weak-Links of Topological Crystalline Insulators Invited Speaker: James Williams Topological Crystalline Insulators (TCI) produce topological states of matter that rely on crystalline symmetry, opening new avenues to create and control the novel properties of the surface state. In this talk I will elucidate the properties of Josephson junctions that use SnTe -- a candidate TCI material -- as the weak link. Deviations from conventional junction properties are observed, including signatures of broken time reversal symmetry. The genesis of these effects, which arise from a confluence of multiple electronic bands, ferroelectric distortions and topology, will be detailed. |
Tuesday, March 3, 2020 3:06PM - 3:18PM |
J60.00002: Fusion and parity readout of Majorana bound states in lateral S-TI-S Josephson junctions Jessica Montone, Guang Yue, Gilbert Arias, Xiong Yao, Deepti Jain, Jisoo Moon, Seongshik Oh, Dale J Van Harlingen We propose experiments designed to demonstrate the fusion of Majorana bound states (MBS) and to measure their parity in S-TI-S (Superconductor-Topological Insulator-Superconductor) lateral Josephson junctions. These junctions are expected to host MBS at Josephson vortex cores where the phase difference across the junction is an odd multiple of π. Our approach is to integrate Al-AlOx-Al single-electron transistors, which are sensitive to the parity of the MBS pairs, with Nb-Bi2Se3-Nb Josephson junctions, in which the MBS can be created and manipulated to carry out fusion and braiding operations. We report progress toward implementing these schemes and incorporating them into circuits for quantum information processing. |
Tuesday, March 3, 2020 3:18PM - 3:30PM |
J60.00003: Interfacial effects of proximitizing superconductivity in topological insulators Ilan Rosen, Molly P Andersen, Linsey Rodenbach, Peng Zhang, Lixuan Tai, Gen Yin, Marc A. Kastner, Kang L. Wang, David Goldhaber-Gordon The proximitization of superconductivity into time-reversal invariant topological insulators, as well as their magnetic counterparts, has produced exciting observations including anomalous Fraunhofer patterns[1, 2], finite momentum pairing[3], and fractional quantized conductances[4]. Yet even as the quality of topological materials rapidly improves, variations in behavior across different experiments and groups are not well understood. We postulate that the properties of the interface between superconducting metals and topological insulators play a key role, and we discuss our attempts to characterize and manipulate such interfaces, focusing on the (BiSb)2Te3 family of topological insulators. |
Tuesday, March 3, 2020 3:30PM - 3:42PM |
J60.00004: Interface and scattering potentials in topological insulator-superconductor heterostructures Eklavya Thareja, Ilya Vekhter Many proposed applications of topological insulators rely on coupling them to superconductors in Josephson-type geometry. However, interface potentials at the boundary between a superconductor and a topological insulator can alter the dispersion and the spin texture of the topological states, thereby changing the nature of the proximity-induced superconducting order. Using effective low-energy models we study how these potentials, combined with the scattering at lateral junctions between superconducting and non-superconducting regions, change the spectra of the Andreev bound states and the Josephson current-phase relationship. We discuss the relevance of our findings to proposals for functional heterostructures. |
Tuesday, March 3, 2020 3:42PM - 3:54PM |
J60.00005: Superconductivity in Sn1-xInxTe thin films grown by molecular beam epitaxy Andrea Bliesener, Junya Feng, Alexey A Taskin, Yoichi Ando Sn1-xInxTe is derived from the topological crystalline insulator SnTe which becomes superconducting when doped with Indium and it is one of the top candidates for topological superconductivity [1]. |
Tuesday, March 3, 2020 3:54PM - 4:06PM |
J60.00006: Superconductivity of Topological Surface States and Strong Proximity Effect in Sn1-
xPbxTe-Pb Heterostructures Jinfeng Jia, Hao Yang, Yao-Yi Li, Teng-Teng Liu, Dandan Guan, Shi-Yong Wang, Hao Zheng, Canhua Liu, Liang Fu Superconducting topological crystalline insulators are expected to form a new type of topological superconductors to host Majorana zero modes under the protection of lattice symmetries. The bulk superconductivity of topological crystalline insulators has been induced through chemical doping and proximity effect. However, only conventional full gaps are observed, so the existence of topological superconductivity in topological crystalline insulators is still controversial. Here, we report the successful fabrication of atomically flat lateral and vertical Sn1-xPbxTe-Pb heterostructures by molecular beam epitaxy. The superconductivity of the Sn1-xPbxTe-Pb heterostructures can be directly investigated by scanning tunneling spectroscopy. Unconventional peak-dip-hump gap features and fourfold symmetric quasiparticle interference patterns taken at the zero energy support the presence of the topological superconductivity in superconducting Sn1-xPbxTe. Strong superconducting proximity effect and easy preparation of various constructions between Sn1-xPbxTe and Pb make the heterostructures to be a promising candidate for topological superconducting devices to detect and manipulate Majorana zero modes in the future. |
Tuesday, March 3, 2020 4:06PM - 4:18PM |
J60.00007: Probing the location of Josephson vortices and the Majorana states bound to them in S-TI-S lateral Josephson junctions via Scanning SQUID Microscopy Gilbert Arias, Jessica Montone, Erik D Huemiller, Guang Yue, Dale J Van Harlingen Superconducting-Topological Insulator-Superconducting (S-TI-S) Josephson junctions are a promising platform for creating and manipulating Majorana bound states (MBS). The MBS are localized at the cores of Josephson vortices where the phase difference across the junction is an odd-multiple of π. They can be manipulated by applying fields and currents to carry out braiding operations for quantum information processing. To optimize braiding protocols, it is useful to track the motion of the vortices via local magnetic imaging. We are developing a Scanning SQUID Microscope in which the probe is a superconducting pickup loop with submicron dimensions. It is inductively-coupled to a commercial dc SQUID, providing the required field sensitivity and spatial resolution. In this talk, we report our progress towards imaging the Josephson vortices and the currents carried by the Majorana states. |
Tuesday, March 3, 2020 4:18PM - 4:30PM |
J60.00008: Excess Vortex-Vortex Supercurrent as Method for Readout of Majorana Parity in Fe(Se,Te) Benjamin November, Jay Sau, James Williams, Jennifer E. Hoffman Topological superconductors are one of the most exciting new platforms for the development of topological quantum computing. Specifically, the Fe(Se,Te) family has been shown to host Majorana zero-energy modes (MZMs) in vortex cores [1], pairs of which can potentially be used as topologically protected qubits. However, there has been no previous calculations to suggest that the two distinct parity states can be distinguished experimentally. Through the use of an effective two-dimensional Fu-Kane model on the surface of FeTexSe1-x, we approximate the (px + ipy) superconductor as an internal s-wave proximity effect on the topological surface states. We then numerically calculate the wavefunction solution to the resulting Bogoliubov-de Gennes equation for both spatially separated single vortices and the double vortex limit of complete overlap of the single vortex pair. Using these wavefunction solutions, we compute supercurrent generated by zero-energy mode splitting and the resulting magnetic field gradient above the surface. We conclude it is possible to measure the presence of this excess supercurrent, and thus the quantum state of the MZM pair, using magnetic force microscopy. |
Tuesday, March 3, 2020 4:30PM - 4:42PM |
J60.00009: Proximity effect at the superconducting-topological insulator interface from first principles Kyungwha Park, Balazs Ujfalussy A topological insulator (TI) film in contact with an s-wave superconducting |
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J60.00010: Multiple Pairs of Propagating Majorana Modes in the Votex Line of Superconducting Quadratic Dirac Semimetals Lun Hu, Shengshan Qin, Chen Fang, Jiangping Hu, Fu-Chun Zhang We study the vortex bound states in a class of three dimensional (3D) time reversal invariant quadratic Dirac semimetals. Assuming intrinsic s-wave superconductivity, we find that multiple Majorana modes can be bound to the vortex line for certain range of doping level. Specifically, due to the quadratic Dirac points in the band structures, quasi-1D Majorana modes carrying angular momentum ±1 and ±2 can propagate along the vortex line; for quadratic Dirac semimetals with nontrival Z2 topological character, additional 0D Majorana zero modes carrying angular momentum 0 can be bound at the end of the vortex line. Together with our work in linear Dirac semimetals (Phys. Rev. Lett. 123, 027003), we establish a complete correspondence between the topological properties of the normal state band structures and the vortex bound states in the s-wave superconducting state. |
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