Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session E1: Recent Developments in Hybrid Semiconductor-Superconductor JunctionsInvited
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Sponsoring Units: DCMP Chair: Yong Chen, Purdue University Room: Ballroom I |
Tuesday, March 15, 2016 8:00AM - 8:36AM |
E1.00001: Finite Momentum Pairing and Spatially Varying Order Parameter in Proximitized HgTe Quantum Wells Invited Speaker: Amir Yacoby Conventional s-wave superconductivity is understood to arise from singlet pairing of electrons with opposite Fermi momenta, forming Cooper pairs whose net momentum is zero. Several recent studies have focused on structures where such conventional s-wave superconductors are coupled to systems with an unusual configuration of electronic spin and momentum at the Fermi surface. Under these conditions, the nature of the paired state can be modified and the system may even undergo a topological phase transition. Here we present measurements and theoretical calculations of several HgTe quantum wells coupled to either aluminum or niobium superconductors and subject to a magnetic field in the plane of the quantum well. By studying the oscillatory response of Josephson interference to the magnitude of the in-plane magnetic field, we find that the induced pairing within the quantum well oscillates between singlet and triplet pairing and is spatially varying. Cooper pairs acquire a tunable momentum that grows with magnetic field strength, directly reflecting the response of the spin-dependent Fermi surfaces to the in-plane magnetic field. Our new understanding of the interplay between spin physics and superconductivity introduces a way to spatially engineer the order parameter, as well as a general framework within which to investigate electronic spin texture at the Fermi surface of materials. [Preview Abstract] |
Tuesday, March 15, 2016 8:36AM - 9:12AM |
E1.00002: S-TI-S Josephson junction networks: a platform for exploring and exploiting topological states and Majorana fermions Invited Speaker: Dale J Van Harlingen We are studying the transport properties of hybrid superconductor-topological insulator nanoscale devices fabricated by depositing superconductor electrodes onto the surface of topological insulators. In top-gated lateral Nb-Bi$_{\mathrm{2}}$Se$_{\mathrm{3}}$-Nb junctions, we have measured the Josephson supercurrent and conductance as a function of geometry, temperature, and gate voltage in order to determine the nature of the electronic transport. The supercurrent exhibits a sharp drop as a function of gate voltage that may be explained by the relocation of the topological surface state from above to below trivial conducting surface states formed by band-banding near the surface. We find that the magnetic field modulation of the supercurrent in Josephson junctions and dc SQUIDs exhibits anomalous features consistent with a 4$\pi $-periodic sin($\varphi $/2)-component in the junction current-phase relation that may arise from the nucleation of Majorana bound states in the junction. We are exploring circuits for imaging, manipulating, and braiding these exotic excitations and schemes for reading out their parity. In collaboration with Aaron Finck, Erik Huemiller, Cihan Kurter, Vladimir Orlyanchik, Martin Stehno, and Can Zhang. [Preview Abstract] |
Tuesday, March 15, 2016 9:12AM - 9:48AM |
E1.00003: Induced superconductivity in high mobility two dimensional electron gas in GaAs heterostructures Invited Speaker: Leonid P. Rokhinson Search for Majorana fermions renewed interest in semiconductor-superconductor interfaces, while a quest for higher order non-Abelian excitations demands formation of superconducting contacts to materials with fractionalized excitations, e.g. a two-dimensional electron gas in a fractional quantum Hall regime. Here we report induced superconductivity in high mobility two-dimensional electron gas in GaAs heterostructures and development of highly transparent semiconductor-superconductor ohmic contacts. Supercurrent with characteristic temperature dependence of a ballistic junction has been observed across 0.6 $\mu$m, a regime previously achieved only in point contacts but essential to the formation of well separated non-Abelian states. High critical fields ($>16$ Tesla) in NbN contacts enables investigation of an interplay between superconductivity and strongly correlated states in a two dimensional electron gas at high magnetic fields. [Preview Abstract] |
Tuesday, March 15, 2016 9:48AM - 10:24AM |
E1.00004: Proximity induced topological superconductivity and Majorana fermions Invited Speaker: Carlo Beenakker Topological states of matter are a source of low-energy quasiparticles, bound to a defect or propagating along the surface. In a superconductor these are Majorana fermions, described by a real rather than a complex wave function. The absence of complex phase factors promises protection against decoherence in quantum computations based on topological superconductivity. The early theoretical models that produced Majorana fermions relied on an exotic superconducting order, with spin-triplet Cooper pairs in a chiral $p$-wave orbital state. A recent alternative is to start from a conventional spin-singlet superconductor and use the proximity effect to induce a topologically nontrivial superconducting state in a material with strong spin-orbit coupling. In this talk we give an overview of some of the manifestations of a real Majorana wave function that are waiting to be observed. In particular, we discuss how shot noise measurements can provide for a purely electrical method of detection of charge-neutral Majorana edge modes. [Preview Abstract] |
Tuesday, March 15, 2016 10:24AM - 11:00AM |
E1.00005: Milestones toward Majorana-based quantum computing Invited Speaker: Jason Alicea Experiments on nanowire-based Majorana platforms now appear poised to move beyond the preliminary problem of zero-mode detection and towards loftier goals of realizing non-Abelian statistics and quantum information applications. Using an approach that synthesizes recent materials growth breakthroughs with tools long successfully deployed in quantum-dot research, I will outline a number of relatively modest milestones that progressively bridge the gap between the current state of the art and these grand longer-term challenges. The intermediate Majorana experiments surveyed in this talk should be broadly adaptable to other approaches as well. [Preview Abstract] |
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