Microwave absorption by vortex cores in the high-temperature superconductor YBa2Cu3O7-x.

Abstract

Direct absorption measurements of microwave energy having energy less than the superconducting gap in the granular composites of the 90-K superconductor ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$ as a function of dc magnetic-field strength between 0.1 and 1.0 T reveal a nonlinearly increasing absorption of microwave energy with increasing field strength. The absorption can be detected in regions of the T-H phase diagram in which thermally activated flux flow does not occur. The temperature and field dependences of the absorption are different from those for low-magnetic-field absorption (H0.06 T) and are shown to be consistent with the behavior expected by the absorption of microwave energy by normal carriers at the cores of vortices in type-II superconducting materials.