Scaling of current-resistivity isotherms of indium films in a magnetic field

Abstract

We have studied the nonlinear resistivity ( J- ϱ characteristics) of granular indium films with differennt thickness t and grain size d in various constant magnetic fields B down to 0.6 K. Films 1 and 2 with d=14 nm are viewed as a dirty superconductor while films 3 and 4 with d = 28 nm are modeled as a random Josephson network. The J- ϱ data are analyzed according to the vortex-glass (VG) theory. For film 1 with t = 100 nm , we have obtained the VG transition temperatures T g( B) and scaling functions, which are similar to those obtained in high- T c superconductors, suggesting that the VG transition also takes place in a conventional superconductor with sufficiently low T c (< 4 K). A finite-size effect is visible for thinner film 2 with t=20 nm , where T g appears to be zero. This is in accord with the two-dimensional (2D) VG theory. The VG behavior is not observed for films 3 ( t = 60 nm) and 4 ( t = 200 nm) with d = 28 nm . We ascribe it to the fact that the measuring current is too large to probe the film at lengths larger than d = 28 nm .