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 Tc. We have studied magnetic excitations in \bis single crystals above Tc with the method of surface spin decoration. The surface layer of diphenyl-picrylhydrazyl was used as a sensitive probe of magnetic field distortions. The temperature dependence of the ESR signal parameters has indicated that far above Tc the magnetic flux of a sample is affected by the superconducting order parameter fluctuations while close to Tc its changes are due to vortex-type excitations.
@article{arxiv.1002.1029,
title = {Vortex excitations above T_c as revealed by ESR},
author = {Yu. Talanov and L. Salakhutdinov and E. Giannini and R. Khasanov},
journal= {arXiv preprint arXiv:1002.1029},
year = {2010}
}