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.
Highlights
To understand better the individual behavior of superconducting vortices under the influence of an in plane ac magnetic field, we have simulated the TDGL equation in 3D
We investigated two types of samples: plain 60 nm thick Pb films ðTc^7:2KÞ and 60 nm thick Pb films deposited over a square array of periodic pinning centers (PbPPC), consisting of circular Py dots
The broadband measurements were done with a Vector Network Analyzer (VNA) connected to a coplanar waveguide (CPW) situated inside a cryostat with a superconducting magnet
Summary
To understand better the individual behavior of superconducting vortices under the influence of an in plane ac magnetic field, we have simulated the TDGL equation in 3D. Simulations allow to include a DC field perpendicular to the film to create vortices, and a sinusoidal field parallel to the plane that represents the mw field generated by the CPW. Both field components are introduced through the appropriate boundary conditions (see Suplementary material). Future work could try to analyze numerically possible coupled magnetic dot-superconducting vortex dynamics. This task, presents great challenge because of the need to include dynamics of magnetic pinning cente
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