Vortex excitations above T_c as revealed by ESR

TL;DR

This study uses ESR to detect magnetic vortices in high-temperature superconductors above T_c, revealing vortex excitations and fluctuations related to the superconducting order parameter.

Contribution

First direct evidence of vortex excitations above T_c in high-temperature superconductors using ESR and surface spin decoration techniques.

Findings

Detection of magnetic vortices above T_c

ESR signal changes indicate vortex-type excitations

Magnetic flux affected by order parameter fluctuations above T_c

Abstract

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 $T_c$. We have studied magnetic excitations in \bis single crystals above $T_c$ 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 $T_c$ the magnetic flux of a sample is affected by the superconducting order parameter fluctuations while close to $T_c$ its changes are due to vortex-type excitations.