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

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