The 2D–3D crossover and anisotropy of upper critical fields in Nb and NbN superconducting thin films

摘要

Highlights?Detailed investigation of the upper critical field behavior, as measured resistively, of Nb and NbN superconducting thin films with varying thickness.?The thin films exhibit 2D–3D crossover in addition to anisotropic parallel and perpendicular upper critical fields, which show thickness dependence.?The observed behavior of dimensional crossover and anisotropy is understood using Ginzburg–Landau approach.AbstractThe upper critical field (Bc2) of superconducting thin films of Nb (film thicknessd?= 40?nm) and NbN (d?= ?10, 50 and 100?nm) have been measured and analyzed as a function of temperature (T?=?1.8–15?K) in both parallel and perpendicular magnetic field (B?= ?0–7?T) directions with respect to th