Magnetic fluctuations and superconductivity in Fe pnictides probed by electron spin resonance

TL;DR

This study uses electron spin resonance to investigate magnetic fluctuations and superconductivity in Eu_{0.5}K_{0.5}Fe_2As_2, revealing Fermi-liquid behavior and magnetic fluctuations near the superconducting transition.

Contribution

It demonstrates ESR as a probe for magnetic fluctuations and superconductivity in Fe pnictides, highlighting deviations from Fermi-liquid behavior near T_C.

Findings

Korringa-like linear increase of 1/T_1^{ESR} above T_C

Enhanced magnetic fluctuations near 45 K

Power-law T^{1.5} relaxation below T_C

Abstract

The electron spin resonance absorption spectrum of Eu^{2+} ions serves as a probe of the normal and superconducting state in Eu_{0.5}K_{0.5}Fe_2As_2. The spin-lattice relaxation rate 1/T_1^{\rm ESR} obtained from the ESR linewidth exhibits a Korringa-like linear increase with temperature above T_C evidencing a normal Fermi-liquid behavior. Below 45 K deviations from the Korringa-law occur which are ascribed to enhanced magnetic fluctuations within the FeAs layers upon approaching the superconducting transition. Below T_C the spin-lattice relaxation rate 1/T_1^{\rm ESR} follows a T^{1.5}-behavior without the appearance of a coherence peak.