Microwave-stimulated superconductivity due to presence of vortices

TL;DR

This paper demonstrates that GHz radiation can enhance superconductivity in type II superconductors with vortices, reducing vortex core size and dissipation, supported by experiments and numerical simulations.

Contribution

It provides the first experimental evidence of microwave-stimulated superconductivity involving vortices in type II superconductors, with detailed analysis of vortex dynamics.

Findings

Superconductivity is enhanced by GHz radiation in Pb films with vortices.

Vortex core size decreases under microwave stimulation, reducing dissipation.

Stimulated regime shows increased upper critical field and altered vortex behavior.

Abstract

The response of superconducting devices to electromagnetic radiation is a core concept implemented in diverse applications, ranging from the currently used voltage standard to single photon detectors in astronomy. Suprisingly, a sufficiently high power subgap radiation may stimulate superconductivity itself. The possibility of stimulating type II superconductors, in which the radiation may interact also with vortex cores, remains however unclear. Here we report on superconductivity enhanced by GHz radiation in type II superconducting Pb films in the presence of vortices. The stimulation effect is more clearly observed in the upper critical field and less pronounced in the critical temperature. The magnetic field dependence of the vortex related microwave losses in a film with periodic pinning reveals a reduced dissipation of mobile vortices in the stimulated regime due to a reduction of the core size. Results of numerical simulations support the validy of this conclusion. Our findings may have intriguing connections with holographic superconductors in which the possibility of stimulation is under current debate.