Linear ac response of thin superconductors during flux creep

The linear magnetic susceptibility chi(omega) of superconducting strips and disks in a transverse magnetic field is calculated in the flux-creep regime. It is shown that chi(omega) = chi' - i chi '' for omega >> 1/t is universal, independent of temperature, de field, and material parameters, depending only on the sample shape, ac frequency omega/2 pi, and time t elapsed after creep has started. Qualitatively, chi(omega) can be obtained from the chi(omega) of metallic conductors by replacing the Ohmic relaxation time by t. At wt >> 1, which may apply down to rather low frequencies, the dissipative flux-creep state exhibits a nearly Meissner-like response with chi' = -1 + 0.40/omega t and chi '' = 0.251n(29 omega t)/omega wt for disks.