A simple non-vortex model of the fundamental AC susceptibility of granular superconductors

Abstract

We model a granular superconductor as a single loop of adjacent grains having a characteristic temperature-dependent electrical resistance and a temperature-independent inductance. Using first principles, without assuming the existence of vortices, the fundamental AC susceptibility components were calculated when the loop is immersed in a purely AC magnetic field. The simulated in-phase susceptibility appears as a hump below the transition temperature, while the corresponding out-of-phase susceptibility appears as an intergrain peak. These features broaden and shift to low temperatures when the resistance decreases slowly with decrease in temperature. With increase in the inductance, the magnitudes of the susceptibilities decrease and the intergrain features appear at higher temperatures.