Origin of matching effect in anti-dot array of superconducting NbN thin films

Abstract

We investigate the origin of the matching effect observed in disordered superconducting NbN thin films with a periodic array of holes. In addition to the periodic variation in electrical resistance just above the superconducting transition temperature Tc0, we find pronounced periodic variations with magnetic field in all dynamical quantities that can be influenced by flux-line motion under an external drive, including the magnetic shielding response and the critical current, which survives in some samples down to temperatures as low as 0.09Tc0. In contrast, the superconducting energy gap Δ, which is a true thermodynamic quantity, does not show any periodic variation with magnetic field for the same films. Our results show that commensurate pinning of the flux-line lattice driven by vortex–vortex interaction is the dominant mechanism for the matching effects observed in these superconducting anti-dot films, rather than a Little–Parks-like quantum interference effect.