Linear ac Response of Thin Superconductors during Flux Creep

Ernst Helmut Brandt; Alexander Gurevich

doi:10.1103/PhysRevLett.76.1723

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Linear ac Response of Thin Superconductors during Flux Creep

Ernst Helmut Brandt, Alexander Gurevich

DOI 10.1103/PhysRevLett.76.1723 · Physical Review Letters

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Abstract

The linear magnetic susceptibility χ(ω) of superconducting strips and disks in a transverse magnetic field is calculated in the flux-creep regime. It is shown that χ(ω)=χ′−iχ′′ for ω≫1/t is universal, independent of temperature, dc field, and material parameters, depending only on the sample shape, ac frequency ω/2π, and time t elapsed after creep has started. Qualitatively, χ(ω) can be obtained from the χ(ω) of metallic conductors by replacing the Ohmic relaxation time by t. At ωt≫1, which may apply down to rather low frequencies, the dissipative flux-creep state exhibits a nearly Meissner-like response with χ′=−1+0.40/ωt and χ′′=0.25ln(29ωt)/ωt for disks.