Microwave absorption in the superconducting and normal phases of Y-Ba-Cu-O

Abstract

Microwave absorption in a dc magnetic field up to 12 kG, attributed to nonequilibrium contributions to the ac susceptibility, appears at $T_c$ as the sample is cooled. ESR measurements of Y-Ba-Cu-O show that ${\mathrm{Cu}}^{2+}$ exists only in the fraction of the sample which is not superconducting in a distorted octahedral surrounding.