Vortex Excitations Above T in the Cuprate Superconductor BiSrCaCuO as Revealed by ESR.

Using electron spin resonance (ESR) technique we have obtained data evidencing the existence of magnetic vortices in high-temperature superconductors at temperatures above the critical one T. We have studied magnetic excitations in BiSrCaCuO single crystals above T with the method of surface spin decoration. The surface layer of diphenylpicrylhydrazyl was used as a sensitive probe of magnetic field distortions. The temperature dependence of the ESR signal parameters has indicated that far above T the magnetic flux of a sample is affected by the superconducting order parameter fluctuations while close to T its changes are due to vortex-type excitations. [ABSTRACT FROM AUTHOR]