APPLICATION OF A BRIDGE CIRCUIT FOR AN INDUCTIVE CRITICAL-CURRENT DENSITY-MEASUREMENT OF SUPERCONDUCTING THIN-FILMS

Recently, a new contactless J(c) measurement technique by monitoring n onlinear responses from a coil mounted in the proximity of a supercond ucting film was reported by Classen et al. [Rev. Sci. Instrum. 62, 996 (199 1 ) ]. An improved method to measure the nonlinear inductive res ponse is developed using an inductance bridge circuit, which discrimin ates the third-harmonic signal due to the nonlinearity from those of o ther origins. Moreover, in this technique, the phase of the third-harm onic signal can be used to determine the critical current.