Thermally activated dynamics of spontaneous perpendicular vortices tuned by parallel magnetic fields in thin superconducting films

Milind N. Kunchur, Manlai Liang, and Alex Gurevich

Phys. Rev. B 86, 024521 – Published 24 July 2012

Abstract

We report magnetotransport measurements on a superconducting molybdenum-germanium (MoGe) film of thickness $d = 50$ nm in parallel magnetic fields and show evidence of a transition from a Meissner state to a resistive state of spontaneous perpendicular vortices generated by thermal fluctuations above a certain temperature $T > T_{v} (B)$ . Here $T_{v}$ appears to match the vortex core explosion condition $d \approx 4.4 ξ (T_{v})$ , where $ξ$ is the coherence length. For $T > T_{v}$ , we observed that a nonlinear current-voltage ( $I$ - $V$ ) response (Ohmic at low currents and the power law $V \propto I^{β}$ at higher $I$ ) is exponentially dependent on $B^{2}$ . We propose a model in which the resistive state at $T > T_{v}$ is due to thermally activated hopping of spontaneous perpendicular vortices tuned by the pairbreaking effect of the parallel $B$ .