Anomalous suppression of the transition temperature of superconducting nanostructured honeycomb films: Electrical transport measurements and Maekawa-Fukuyama model

Abstract

We report electrical transport measurements made on thin superconducting niobium films perforated by an etched array of nanoscopic holes. The hole diameter in these ``honeycomb'' network films is comparable to the coherence length of the parent superconducting material. A series of 12 films, with varying hole depths, were measured. As the film thickness is decreased, an unusually large reduction of transition temperature is observed for the honeycomb films as compared to plain etched films of similar thicknesses. We report on a ${T}_{c}$ reduction in superconducting network films that is not due to an applied magnetic field. These observations are in contrast to previous reports based on Ginzburg-Landau theory analysis, which does not allow for any change in the transition temperature for perforated films in comparison to plain films. The Maekawa-Fukuyama (MF) model for two-dimensional (2D) superconductors is used to fit the sheet resistance data. The MF-2D model fits very well to the lightly etched samples, but an anomaly in ${T}_{c}$ reduction is observed for heavily etched samples. These deviations are analyzed on the basis of change in dimensionality using the Aslamozov-Larkin model.