Nonlinear electrodynamics and nonresonant microwave absorption in ceramic superconductors

Abstract

We work out some of the consequences of a simple model for nonlinear electrodynamics and nonresonant microwave absorption in the high-temperature superconductors. The model assumes that these materials contain loops of weakly coupled superconducting grains. As the magnetic field is changed, a loop jumps from one energy state to another, thus experiencing phase slips. This produces both electromagnetic absorption through the normal shunt resistance in the junctions, and induced currents at high-order multiples of the applied frequency. The calculated power spectrum from a single loop, with and without a dc applied magnetic field, is in qualitative agreement with the measurements of Jeffries et al. [Phys. Rev. B 37, 9840 (1988)].