Critical current properties of HTSC thin films for applied purposes

Abstract

A contactless method for measurement of critical current J_c and critical temperature T_c was used. J_c was evaluated from an abrupt increase of the third harmonic voltage Var across the coil. System optimization resulted in an extension of the largest detectable current density to 2.5·10⁷ A/cm² at 77 K at a film thickness of 200 nm. The main results are as follows: 1) The curvature of J_c(T) for different films exhibits both positive and negative values; 2) Some samples display two kinks in Var as function of the driving current; 3) J_c changes as a function of film plane coordinates.