59Co-NQR study on superconducting NaxCoO2.yH2O

TL;DR

This study uses 59Co NQR to investigate the superconducting properties of NaxCoO2.yH2O, revealing insights into its magnetic state and implications for its superconducting mechanism.

Contribution

First detailed 59Co NQR analysis of NaxCoO2.yH2O, linking magnetic properties to superconductivity mechanisms.

Findings

Observation of a coherence peak in 1/T1 below Tc

Metallic state closer to ferromagnetic phase than non-superconducting counterpart

Constraints on possible superconducting pairing mechanisms

Abstract

Layered Co oxide NaxCoO2.yH2O with a superconducting transition temperature Tc =4.5 K has been studied by 59Co NQR. The nuclear spin relaxation rate 1/59T1 is nearly proportional to temperature T in the normal state. In the superconducting state, it exhibits the coherence peak and decreases with decreasing T below ~0.8Tc. Detailed comparison of the 1/T1T values and the magnetic susceptibilities between NaxCoO2.yH2O and NaxCoO2 implies that the metallic state of the former system is closer to a ferromagnetic phase than that of the latter. These experimental results impose a restriction on the mechanism of the superconductivity.