NMR investigation of vortex dynamics in Ba(Fe0.93Rh0.07)2As2 superconductor

TL;DR

This study uses 75As NMR techniques to investigate vortex dynamics in Ba(Fe0.93Rh0.07)2As2 superconductor, revealing flux line motions and pinning characteristics below the critical temperature, with field orientation affecting observed relaxation peaks.

Contribution

First NMR-based analysis of vortex dynamics in this superconductor, identifying flux line motion peaks and pinning energies with a thermally activated vortex model.

Findings

Peak in relaxation rates suppressed when magnetic field is parallel to ab plane.

Flux line motions are thermally activated and influence NMR linewidth and relaxation.

Pinning energy barriers are quantified from relaxation data.

Abstract

75As NMR spin-lattice relaxation (1/T1) and spin-echo decay (1/T2) rate measurements were performed in a single crystal of Ba(Fe0.93Rh0.07)2As2 superconductor. Below the superconducting transition temperature Tc, when the magnetic field H is applied along the c axes, a peak in both relaxation rates is observed. Remarkably that peak is suppressed for H || ab. Those maxima in 1/T1 and 1/T2 have been ascribed to the flux lines lattice motions and the corresponding correlation times and pinning energy barriers have been derived on the basis of an heuristic model. Further information on the flux lines motion was derived from the narrowing of 75As NMR linewidth below Tc and found to be consistent with that obtained from 1/T2 measurements. All the experimental results are described in the framework of thermally activated vortices motions.