Berezinskii–Kosterlitz–Thouless Transition in Ultrathin Niobium Films

Abstract

We use resistivity and current–voltage characteristics measurements to evaluate the impact of the disorder on the nature of the Berezinskii–Kosterlitz–Thouless transition in ultrathin niobium (Nb) films. The films, with thickness in the range of 3.6–8.5 nm, show the structural transition from polycrystalline to amorphous structure upon a decrease in the film thickness. We show that this transformation results in the smearing of the Berezinskii–Kosterlitz–Thouless transition, until eventually the Berezinskii–Kosterlitz–Thouless scenario breaks down due to film inhomogeneity.