75As NMR Observation of Anisotropic Spin Fluctuations in the Ba[(Fe0.92Co0.08)2]2As2 Superconductor (Tc = 22 K)

TL;DR

This study uses 75As NMR to reveal that anisotropic spin fluctuations increase as the temperature approaches Tc in an electron-doped superconductor, contrasting with behavior in cuprates.

Contribution

It provides new insights into the temperature-dependent anisotropic spin fluctuations in Ba(Fe,Co)2As2 superconductors using 75As NMR.

Findings

Anisotropy R of spin fluctuations increases toward Tc.

Stronger spin fluctuations are observed along the c-axis.

Contrasts with temperature-independent R in cuprate superconductors.

Abstract

We demonstrate that the anisotropy R of the paramagnetic spin fluctuations grows toward Tc at 75As sites in the optimally electron-doped superconductor Ba[(Fe0.92Co0.08)2]2As2, with stronger spin fluctuations along the c-axis. Our finding is in remarkable contrast with the case of high T$_c$ cuprates, where R is independent of temperature above Tc.