Fluctuation conductance and the Berezinskii-Kosterlitz-Thouless transition in two dimensional epitaxial NbTiN ultra-thin films

Abstract

We study on the electric transport properties of epitaxial NbTiN ultrathin films in a range from 2 to 8nm. The films with 4 nm thick shows superconductivity of which mean-field superconducting transition temperature is Tc0 = 9.43 K The excess conductance due to superconducting fluctuations was measured at temperatures above Tc0. The paraconductivity shows a two-dimensional like behaviour at close to T c0. Experimental results are in good agreement with the sum of Aslamazov - Larkin and Maki - Thompson term for superconducting fluctuation theory. Decreasing temperature below Tc0, the current-voltage characteristic shows a crossover from linear to nonlinear behaviour. The exponent α of current-voltage relation, V ∼ Iα showed universal jump at TcBKT = 9.33 K As results, we find that there is a consistency between the parametrization of the2D characteristics of fluctuation paraconductivity above Tc0 and Berezinskii-Kosterlitz- Thouless type behaviour below Tc0. © Published under licence by IOP Publishing Ltd.