Stochastic resonance phenomenon in a superconducting surface state of single-crystal Nb

Abstract

We report an experimental observation of a stochastic resonance pheomenon in single-crystal Nb. Measurements of the nonlinear susceptibility of Nb ${(T}_c\approx 9.15\hspace{0.5em}\mathrm{K})$ have been performed as a function of temperature, and applied dc and ac fields. The latter consist of a high-frequency signal with an amplitude modulation at low-frequency. Nonmonotonic changes of the nonlinear response have been found as a function of the dc and ac fields in a surface superconducting state of Nb. The theoretical analysis based on the two level model of a stochastic resonance phenomenon provides a qualitative explanation of the experimental results.