Normal metal - insulator - superconductor interferometer

TL;DR

This paper reports on the fabrication and measurement of a hybrid normal metal-insulator-superconductor interferometer, revealing unusual magnetic flux oscillation periods that challenge existing theoretical understanding.

Contribution

It introduces a novel hybrid interferometer structure and observes unexpected flux oscillation periods, highlighting phenomena not explained by current theories.

Findings

Periodic oscillations of tunnel current with magnetic field observed

Oscillation period exceeds standard flux quantum values

Temperature affects the amplitude and period of oscillations

Abstract

Hybrid normal metal - insulator - superconductor microstructures suitable for studying an interference of electrons were fabricated. The structures consist of a superconducting loop connected to a normal metal electrode through a tunnel barrier . An optical interferometer with a beam splitter can be considered as a classical analogue for this system. All measurements were performed at temperatures well below 1 K. The interference can be observed as periodic oscillations of the tunnel current (voltage) through the junction at fixed bias voltage (current) as a function of a perpendicular magnetic field. The magnitude of the oscillations depends on the bias point. It reaches a maximum at energy $eV$ which is close to the superconducting gap and decreases with an increase of temperature. Surprisingly, the period of the oscillations in units of magnetic flux $\Delta \Phi$ is equal neither to $h/e$ nor to $h/2e$, but significantly exceeds these values for larger loop circumferences. The origin of the phenomena is not clear.