$^{75}$As NMR studies of superconducting LaO$_{0.9}$F$_{0.1}$FeAs

TL;DR

This study uses 75As NMR to investigate the electronic and superconducting properties of LaO0.9F0.1FeAs, revealing gap nodes, spin-singlet pairing, and anisotropic vortex effects.

Contribution

First NMR investigation of LaO0.9F0.1FeAs revealing gap symmetry, pairing nature, and vortex-induced relaxation anisotropy.

Findings

Evidence for line nodes in the superconducting gap.

Confirmation of spin-singlet pairing.

Anisotropic relaxation rates linked to vortex dynamics.

Abstract

We have performed 75As Nuclear Magnetic Resonance (NMR) measurements on aligned powders of the new LaO0.9F0.1FeAs superconductor. In the normal state, we find a strong temperature dependence of the spin shift and Korringa behavior of the spin lattice relaxation rate. In the superconducting state, we find evidence for line nodes in the superconducting gap and spin-singlet pairing. Our measurements reveal a strong anisotropy of the spin lattice relaxation rate, which suggest that superconducting vortices contribute to the relaxation rate when the field is parallel to the c-axis but not for the perpendicular direction.