59Co-NMR Knight Shift of Superconducting Three-Layer NaxCoO2.yH2O

TL;DR

This study uses 59Co-NMR to investigate the superconducting state of three-layer NaxCoO2.yH2O, revealing spin susceptibility suppression consistent with singlet pairing, similar to two-layer variants.

Contribution

First NMR analysis of three-layer NaxCoO2.yH2O showing spin susceptibility behavior and pairing symmetry comparable to two-layer systems.

Findings

Spin susceptibility decreases below Tc for a principal in-plane direction.

Superconducting properties are similar between three-layer and two-layer NaxCoO2.yH2O.

Evidence supports singlet pairing in the three-layer compound.

Abstract

The superconducting state of NaxCoO2.yH2O with three CoO2 layers in a unit cell has been studied by 59Co-NMR. The Knight shift measured for a peak of the NMR spectra corresponding to the external magnetic field H along one of the principal directions within the CoO2 plane, exhibits a rapid decrease with decreasing temperature T below the superconducting transition temperature Tc, indicating that the spin susceptibility is suppressed in the superconducting phase, at least, for this field direction. Because differences of the superconducting properties are rather small between this three-layer NaxCoO2.yH2O and previously reported NaxCoO2.yH2O with two CoO2 layers within a unit cell, the present result of the Knight shift studies indicates that the Cooper pairs of the former system are in the singlet state as in the latter, for which the spin susceptibility is suppressed for both directions of H parallel and perpendicular to the CoO2 plane.