Thickness dependence of the flux-flow velocity and the vortex instability in nanocrystalline γ-Mo2N thin films

Abstract

The influence of the thickness on the vortex instability of nanocrystalline γ-Mo2N thin films is analyzed. The samples were grown on Si (100) using reactive sputtering. The quasiparticle relaxation time for films with thickness between 7 and 26 nm is analyzed in the framework of Larkin–Ovchinnikov instability by performing current-voltage curves. Considering self-heating effects due to finite heat removal from the substrate, we determine a fast quasiparticle relaxation time τ ≈ 50 ps for all the samples at low temperatures. On the other hand, close to Tc, the vortex velocity becomes magnetic field-independent, and τ increases from ≈ 40 to 110 ps as the films are made thicker. The results are discussed considering the disorder's contribution and the bridges' geometry on the vortex instability.