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

The influence of the thickness on the vortex instability of nanocrystalline gamma-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 tau asymptotic to 50 ps for all the samples at low temperatures. On the other hand, close to Tc, the vortex velocity becomes magnetic field-independent, and tau increases from asymptotic to 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.