Tunneling spectroscopy of persistent currents in superconducting microrings

TL;DR

This paper demonstrates that tunneling spectroscopy in superconducting microrings can detect persistent currents through magnetic field-induced oscillations in tunnel current, revealing effects of metastable states and vorticity.

Contribution

It introduces a novel method to probe persistent currents in superconducting rings via tunneling measurements, highlighting the influence of metastable states and vorticity on the current.

Findings

Oscillations of tunnel current depend on magnetic field and bias voltage.

Oscillation period exceeds h/e and h/2e values for larger rings.

Persistent currents modulate the superconducting density of states.

Abstract

It is shown that in a structure consisting of a superconducting ring-shaped electrode overlapped by a normal metal contact through a thin oxide barrier, measurements of the tunnel current in magnetic field can probe persistent currents in the ring. The effect manifests itself as periodic oscillations of the tunnel current through the junction at a fixed bias voltage as function of perpendicular magnetic field. The magnitude of oscillations depends on bias point. It reaches maximum at energy eV which is close to the superconducting gap and decreases with increase of temperature. The period of oscillations dF in units of magnetic flux is equal neither to h/e nor to h/2e, but significantly exceeds these values for larger loop circumferences. The phenomenon is explained by formation of metastable states with large vorticity. The pairing potential and the superconducting density of states are periodically modulated by the persistent currents at sub-critical values resulting in corresponding variations of the measured tunnel current.