Andreev Interferometers in a Strong Radio Frequency Field

TL;DR

This study investigates how 1-40 GHz RF radiation affects the resistance of Andreev interferometers, revealing phase shifts and oscillations linked to RF amplitude and temperature changes, with some unexplained phenomena.

Contribution

It provides experimental insights into RF effects on Andreev interferometers, highlighting phase shifts and resistance oscillations, and emphasizes the need for a microscopic theoretical model.

Findings

Resistance oscillates with magnetic flux at low RF amplitudes.

RF amplitude induces a pi-shift in resistance oscillations.

Response time of the interferometer is estimated to be less than 40 ps.

Abstract

We experimentally study the influence of 1-40 GHz radiation on the resistance of normal (N) mesoscopic conductors coupled to superconducting (S) loops (Andreev interferometers). At low RF amplitudes we observe the usual h/2e superconducting-phase-periodic resistance oscillations as a function of applied magnetic flux. We find that the oscillations acquire a pi-shift with increasing RF amplitude, and consistent with this result the resistance at fixed phase is an oscillating function of the RF amplitude. The results are explained qualitatively as a consequence of two processes. The first is the modulation of the phase difference between the N/S interfaces by the RF field, with the resistance adiabatically following the phase. The second process is the change in the electron temperature caused by the RF field. From the data the response time of the Andreev interferometer is estimated to be <40ps. However there are a number of experimental features which remain unexplained; these include the drastic difference in the behaviour of the resistance at different phases as a function of RF frequency and amplitude, and the existence of a "window of transparency" where heating effects are weak enough to allow for the pi-shift. A microscopic theory describing the influence of RF radiation on Andreev interferometers is required.