Studies on the scaling of fundamental AC susceptibility in high temperature superconductors

Abstract

The fundamental AC susceptibilities (ACS, χ = χ′ - iχ″) of a superconducting slab immersed in an applied DC magnetic field have been calculated by solving the flux diffusion equation. A universal scaling law follows when ACS are measured as a function of AC field amplitude at fixed temperature T in the case of U(j) = U0ln(jc/j). However, the scaling relation fails when ACS are measured as a function of temperature; only the reduced value of χ″/χ″max can be scaled. The calculations also indicate that at large value of U0/kBT, ACS become independent on AC field frequency, and therefore, the critical state can be used to describe ACS in this case. ACS as a function of AC field amplitude and temperature using U(j) = (U0/μ)[(jc/j)μ - 1] have also been calculated; both cannot be scaled, only the reduced value of χ″/χ″max can be scaled.