Superconductivity of Niobium Films

Niobium thin films are prepared by evaporation in ultra-high vacuum system with an electron beam and their superconducting properties are examined as a function of film thickness and temperature. An inflection point appearing in the temperature dependence of the parallel critical field H c // is explained by the temperature dependence of the coherence length ξ( t ). The perpendicular critical field H c ⊥ varies as 1- t independently of their thickness. The coherence length ξ(0) at 0°K of some films are estimated by three methods. Anomalous results that the minimum occurs on the angular dependence of the critical field and the ratio H c // / H c ⊥ becomes lower than 1.69 are discussed by considering the isolated columnar structure.