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29 September 2015

Microwave-stimulated Superconductivity due to Presence of Vortices

Article: published in Scientific Reports by Antonio Lara and Farkhad G. Aliev, IFIMAC researchers and members of the Department of Condensed Matter Physics.

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. [Full article]

The video depicts the changes in size and friction of vortex cores under microwave radiation. At the highest vortex velocity the Larkin-Ovchinnikov (LO) effect (collapse of the vortex) is more pronounced, and the vortex core (blue cylinder) shrinks, reducing the number of normal electrons (green spheres) in it. As it slows down, its size increases again. The friction force (yellow arrow) is weaker at high velocities also, at the center of the periodic motion, also due to the LO effect. Download video

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