Microwave emission from superconducting vortices in Mo/Si superlattices

TL;DR

This study demonstrates microwave emission from vortices in Mo/Si superlattices, showing they can serve as tunable microwave generators bridging RF and terahertz frequencies.

Contribution

It provides the first observation of electromagnetic wave emission from vortices crossing superconductor/insulator superlattices, with tunable spectra in the GHz range.

Findings

Emission spectra show narrow harmonically related peaks.

Emission frequency can be tuned by dc bias current and magnetic field.

Superlattices can act as dc-tunable microwave sources.

Abstract

Most of superconductors in a magnetic field are penetrated by a lattice of quantized flux vortices. In the presence of a transport current causing the vortices to cross sample edges, emission of electromagnetic waves is expected due to the continuity of tangential components of the fields at the surface. Yet, such a radiation has not been observed so far due to low radiated power levels and lacking coherence in the vortex motion. Here, we report emission of electromagnetic waves from vortices crossing the layers of a superconductor/insulator Mo/Si superlattice. The emission spectra consist of narrow harmonically related peaks which can be finely tuned in the GHz range by the dc bias current and, coarsely, by the in-plane magnetic field value. Our findings show that superconductor/insulator superlattices can act as dc-tunable microwave generators bridging the frequency gap between conventional radiofrequency oscillators and (sub-)terahertz generators relying upon the Josephson effect.