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 B52: Topological Superconductivity: Planar Josephson JunctionsFocus Live
|
Hide Abstracts |
Sponsoring Units: DMP Chair: Peng Wei, University of California, Riverside |
Monday, March 15, 2021 11:30AM - 11:42AM Live |
B52.00001: Probing the current phase relation of Josephson junctions in an InSbAs 2-dimensional electron gas Chung-Ting Ke, Christian Moehle, Candice Thomas, Di Xiao, Mario Lodari, Vincent van de Kerkhof, Ruben Termaat, Saurabh Karwal, Charles Guinn, Raymond Kallaher, Geoffrey C. Gardner, Giordano Scappucci, Michael Manfra, Srijit Goswami A superconducting quantum interference device (SQUID) is often used to probe the current-phase relationship (CPR) of a Josephson junction by controlling the phase difference across the junction of interest. In a material with strong spin-orbit coupling, tuning this phase difference to π is expected to result in topological superconductivity. We study SQUIDs in a hybrid Al/InSbAs 2-dimensional electron gas, a material with large spin-orbit coupling and g-factor. We simultaneously measure the CPR and perform tunneling spectroscopy at the edge of the junction to probe the Andreev bound states. We also study the evolution of the CPR and Andreev spectrum by changing the carrier density and in-plane magnetic field. |
Monday, March 15, 2021 11:42AM - 12:18PM Live |
B52.00002: Topology, braiding, and disorder in planar Josephson junctions Invited Speaker: Ady Stern In this talk I will describe how the Josephson effect may be employed to realize one dimensional topological superconductivity, with the Josephson phase difference being a "user-friendly" knob to drive the system to become topological. I will describe the basic idea, the experimental observations, the relation to topological superconductivity based on quantum wires, a surprising effect of disorder, and a scheme for braiding Majorana zero modes in Josephson junctions. I will also describe how this system manifests a first order phase transition into a topological phase. |
Monday, March 15, 2021 12:18PM - 12:30PM Live |
B52.00003: Shapiro Steps and Negative Absolute Resistance in Microwave-Driven Shunted Josephson Junctions Bassel Heiba Elfeky, Matthieu Dartiailh, Joseph Yuan, Kaushini S Wickramasinghe, Javad Shabani Topological Josephson junctions (JJs) have been studied as promising candidates to host Majorana fermions, especially because the phase across the junction can be used to tune the topological phase. When a microwave drive is applied to a JJ, it is expected to observe integer and possibly fractional constant voltage steps, Shapiro steps, appearing in the Voltage-Current characteristic due to phase locking. In this work, we observe and study these dynamics in 100nm JJs fabricated on InAs surface quantum wells coupled to epitaxial Al contacts in relation to the applied microwave bias amplitude and frequency as well as an applied external magnetic field. When such nonlinear systems are driven out of equilibrium, exotic behavior such as negative absolute resistance (NAR) could possibly arise that have promising applications in electronics and quantum computing, mainly qubit state manipulation and readout. We discuss these observations in presence of an in-plane magnetic field. |
Monday, March 15, 2021 12:30PM - 12:42PM Live |
B52.00004: Scanning Probe Study of Topological Insulator Josephson Junctions Michael Gottschalk, Guang Yue, Eric Goodwin, Gilbert Arias, Dale J Van Harlingen, Stuart Tessmer We present progress towards testing for Majorana bound states in superconductor-topological insulator (S-TI) heterostructures. In a seminal paper in 2008, Fu and Kane predicted the existence of Majorana bound states in planar S-TI-S Josephson junctions with a phase difference of π. There has since been intensive experimental work to realize this system and look for signatures of Majorana bound states. Our approach is to spectroscopically probe superconducting Nb islands deposited on the topological insulator Bi2Se3, employing both bulk crystals and thin-film materials. The goal is to detect Majorana signatures in Josephson vortices on the surface with scanning probe methods. Scanning tunneling microscopy measurements and numerical simulations will be presented. |
Monday, March 15, 2021 12:42PM - 12:54PM Live |
B52.00005: Topological Superconductivity in Crystalline Anisotropic Josephson Junctions Joseph Pakizer, Benedikt Scharf, Alex Matos Abiague We theoretically investigate the emergence of Topological Superconductivity (TS) in planar JJs [1,2] subject to Rashba and Dresselhaus spin-orbit couplings (SOCs) and in-plane magnetic field. We focus on studying the effects of the junction crystallographic orientation and magnetic field direction on the capability for the system to enter TS and produce a significant topological gap for Majorana bound state (MBS) protection. The ability to electrically tune the topological phase, as well as transitions between BDI and D symmetry classes, has been found to greatly depend on the interplay between SOC strengths, magnetic field and crystallographic orientations [3]. Our findings provide guidelines for optimizing the topological gap protecting MBS in crystalline anisotropic planar JJs, especially in non-collinear junctions [4]. |
Monday, March 15, 2021 12:54PM - 1:06PM Live |
B52.00006: Signatures of flux-dependent Majorana zero modes in a finite-width topological Josephson junction Nick Abboud, Varsha Subramanyan, Xiao-Qi Sun, Suraj S Hegde, Smitha Vishveshwara In the presence of an applied magnetic field, an extended Josephson junction between topological superconductors can host Majorana zero modes (MZMs) in its Josephson vortices. The MZMs in a multiply connected network of such junctions can be moved and braided by applying currents, voltages, and phase differences. We present a theoretical study of MZMs and Josephson currents in a junction between two finite-sized px+ipy superconductor islands, where a key role is played by a delocalized MZM on the system’s outer boundary. Our main result is a parity-dependent splitting of the critical current diffraction pattern. On the way, we characterize the sub-gap quasiparticle spectrum and the equilibrium positions and dynamics of the MZMs under external biases. We connect our results to ongoing experiments on topological superconductors in extended junction geometries, such as those being carried out by the group of Van Harlingen. |
Monday, March 15, 2021 1:06PM - 1:18PM Live |
B52.00007: Dynamics of Majorana Bound States in a thin annular topological Josephson junction Varsha Subramanyan, Nick Abboud, Xiaoqi Sun, Smitha Vishveshwara The Majorana bound states formed in extended SIS Josephson junctions between p+ip superconductors have been popular both as a means of detection of Majorana zero modes as well as designing braiding operations. In this context, we study the topological Josephson junction in annular geometries. In the presence of an external magnetic field, we demonstrate the nucleation of an even number of Majorana bound states and calculate the current contribution stemming from Andreev scattering across the junction. We also discuss possible signatures of these states in critical currents across the junction, and schemes to control the dynamics of these bound states in the junctions via voltage pulses. In doing so, we compare the characteristics of the annular junction with an extended rectangular junction and establish boundary and size effects. |
Monday, March 15, 2021 1:18PM - 1:54PM Live |
B52.00008: Phase Controlled Topological Superconductivity Invited Speaker: Amir Yacoby Topological superconductors can support localized Majorana states at their boundaries. These quasi-particle excitations have non-Abelian statistics that can be used to encode and manipulate quantum information in a topologically protected manner. While signatures of Majorana bound states have been observed in one-dimensional systems, there is an ongoing effort to find alternative platforms that do not require fine-tuning of parameters and can be easily scalable to large numbers of states. Here we present a novel experimental approach towards a two-dimensional architecture. Using a Josephson junction made of HgTe quantum well coupled to thin-film aluminum, we are able to tune between a trivial and a topological superconducting state by controlling the phase difference across the junction and applying an in-plane magnetic field. We determine the topological state of the induced superconductor by measuring the tunneling conductance at the edge of the junction. At low magnetic fields, we observe a minimum in the tunneling spectra near zero bias, consistent with a trivial superconductor. However, as the magnetic field increases, the tunneling conductance develops a zero-bias peak which persists over a range of phases that expands systematically with increasing magnetic fields. Our observations are consistent with theoretical predictions for this system and with full quantum mechanical numerical simulations performed on model systems with similar dimensions and parameters. Our work establishes this system as a promising platform for realizing topological superconductivity and for creating and manipulating Majorana modes and will therefore open new avenues for probing topological superconducting phases in two-dimensional systems. |
Monday, March 15, 2021 1:54PM - 2:06PM Live |
B52.00009: Probing the parity of Majorana bound states in lateral S-TI-S Josephson junctions via SET detectors and fusion operations Jessica Montone, Guang Yue, Gilbert Arias, Xiong Yao, Deepti Jain, Jisoo Moon, Seongshik Oh, Dale J Van Harlingen We propose experiments designed to probe the parity of Majorana bound states (MBS) 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 (SET), 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 braiding operations. We also present a modification to the experiment in which the MBS pairs are combined on an Au quantum dot to demonstrate fusion. We report progress toward implementing these schemes and incorporating them into circuits for quantum information processing. |
Monday, March 15, 2021 2:06PM - 2:18PM Live |
B52.00010: Topological Josephson junctions based on InGaAs quantum wells Kaveh Delfanazari, Llorens Serra, Pengcheng ma, Ian Farrer, David A Ritchie, Hannah Joyce, Michael Joseph Kelly, Charles G Smith Majorana phases emerge as quantized plateaus in the magnetoconductance of the hybrid junctions based on two-dimensional electron gases (2DEG) under fully out-of-plane magnetic fields [1,2]. The large transverse Rashba spin-orbit interaction in 2DEG, together with a strong magneto-orbital effect, yield topological phase transitions to nontrivial phases hosting Majorana modes. Such Majorana modes are formed at the ends of 2DEG-based wires with a hybrid superconductor-semiconductor integrity. Here, we report on the experimental observation of such topological phases in Josephson junctions, based on In0.75Ga0.25As 2DEG, by sweeping out-of-plane magnetic fields of as small as B(mT) < 100 and probing the conductance to highlight the characteristic quantized magnetoconductance plateaus. |
Monday, March 15, 2021 2:18PM - 2:30PM Not Participating |
B52.00011: Asymmetric Fraunhofer Patterns of Bi2Se3 Josephson Junctions Alexander Beach, Nadya Mason Josephson junctions with topological insulators as their weak link (S-TI-S junctions) are predicted to host Majorana fermions, which are key to creating qubits for topologically protected quantum computing. We fabricate a Bi2Se3 junction with NbTi leads and measure the Fraunhofer patterns of the junction in conjunction with applied in-plane fields, in order to observe the expected asymmetry and finite momentum shift effects. Asymmetric Fraunhofer patterns from the sample appear at zero parallel field and up to 1K, and appear in the maps of Bz vs. Bx,y, with aperiodic node spacings, suggesting they originate from the physical shape of the junction. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700