Non-linear vortex dynamics in the mixed state of superconducting a-MoGe and NbN thin films using low-frequency two-coil mutual inductance technique

We use a low-frequency two-coil mutual inductance technique to investigate the non-linear magnetic shielding response of the vortex lattice in two type-II superconducting thin films, namely a very weakly pinned amorphous Molybdenum Germanium (a-MoGe) and a moderate-to-strongly pinned Niobium Nitride (NbN). We observe a strong dependence of the magnetic shielding response of the superconductors arising from the effect of vortex creep, which extends to very low amplitudes of the applied ac current in the primary coil of the two-coil setup. Quantitatively analysing the data, we develop a computational scheme to obtain the intrinsic values of various vortex lattice parameters, like the pinning force constant, the vortex viscosity and the pinning potential, which can get affected due to flux creep even at very low ac drives.