Co NMR shift anomalies and spin dynamics in the normal state of superconducting CeCoIn; Verification of two-dimensional antiferromagnetic spin fluctuations

Sakai, Hironori   ; Baek, S.-H.*; Brown, S. E.*; Ronning, F.*; Bauer, E. D.*; Thompson, J. D.*

We have measured the Knight shifts () and nuclear relaxation times () for Co in CeCoIn under external fields along a and c axes with the goal of establishing the anisotropy of antiferromagnetic (AFM) spin fluctuations (SF). In our approach, we revisit the problem of interpreting anomalies in the relationship between Knight shift and static susceptibility : assuming a single component susceptibility implies a temperature-dependent hyperfine coupling . Once adopted, a known discrepancy between the behaviors of for Co and In(1) sites is eliminated to within experimental uncertainties and the variation with temperature is analyzed within the framework of two-dimensional AFM SF in proximity to a quantum-critical point. Moreover, the ratio indicates easy-plane anisotropy for 40 K, for the heavy-fermion state.