Asymmetric nanowire SQUID: Linear current-phase relation, stochastic switching, and symmetries

A. Murphy, A. Bezryadin

Research output: Contribution to journalArticle

Abstract

We study nanostructures based on two ultrathin superconducting nanowires connected in parallel to form a superconducting quantum interference device (SQUID). The measured function of the critical current versus magnetic field, IC(B), is multivalued, asymmetric, and its maxima and minima are shifted from the usual integer and half integer flux quantum points. We also propose a low-temperature-limit model which generates accurate fits to the IC(B) functions and provides verifiable predictions. The key assumption of our model is that each wire is characterized by a sample-specific critical phase φC defined as the phase difference at which the supercurrent in the wire is the maximum. For our nanowires φC is much greater than the usual π/2, which makes a qualitative difference in the behavior of the SQUID. The nanowire current-phase relation is assumed linear, since the wires are much longer than the coherence length. The model explains single-valuedness regions where only one vorticity value nv is stable. Also, it predicts regions where multiple vorticity values are stable because the Little-Parks (LP) diamonds, which describe the region of stability for each winding number nv in the current-field diagram, can overlap. We also observe and explain regions in which the standard deviation of the switching current is independent of the magnetic field. We develop a technique that allows a reliable detection of hidden phase slips and use it to determine the boundaries of the LP diamonds even at low currents where IC(B) is not directly measurable.

Original languageEnglish (US)
Article number094507
JournalPhysical Review B
Volume96
Issue number9
DOIs
StatePublished - Sep 11 2017

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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