Radiofrequency generation by coherently moving fluxons

TL;DR

This paper demonstrates that coherently moving fluxons in superconductors can generate tunable radiofrequency signals in the 100 MHz to 1.5 GHz range, using nanostructures as RF generators.

Contribution

It introduces a method to generate tunable RF signals via fluxon dynamics in superconducting nanostructures, with experimental detection of the induced AC voltage at the washboard frequency.

Findings

Fluxon motion produces detectable RF signals.

The washboard frequency can be tuned from 100 MHz to 1.5 GHz.

Subharmonics of the washboard frequency are observed.

Abstract

A lattice of Abrikosov vortices in type II superconductors is characterized by a periodic modulation of the magnetic induction perpendicular to the applied magnetic field. For a coherent vortex motion under the action of a transport current, the magnetic induction at a given point of the sample varies in time with a washboard frequency f_WB = v/d, where v is the vortex velocity and d is the distance between the vortices in the direction of motion. Here, by using a spectrum analyzer connected to a 50 nm-wide Au nanowire meander near the surface of a superconducting Nb film we detect an ac voltage induced by coherently moving fluxons. The voltage is peaked at the washboard frequency, f_WB, and its subharmonics, f_TOF = f_WB/5, determined by the antenna width. By sweeping the dc current value, we reveal that f_WB can be tuned from 100 MHz to 1.5 GHz, thereby demonstrating that patterned normal metal/superconductor nanostructures can be used as dc-tunable generators operating in the radiofrequency range.