Nuclear spin-lattice relaxation rate in the D+iD superconducting state: implications for CoO superconductor

TL;DR

This paper calculates the nuclear spin-lattice relaxation rate in the D+iD superconducting state with impurities, showing how impurities induce residual states and T-linear relaxation, supporting the D+iD pairing symmetry in Na$_{0.35}$CoO$_{2} \, y$H$_2$O.

Contribution

It demonstrates that impurity effects in the D+iD superconducting state explain experimental relaxation rates, supporting the pairing symmetry in a cobaltate superconductor.

Findings

Small impurities induce residual density of states.

T-linear relaxation behavior observed at low temperatures.

D+iD pairing symmetry aligns with experimental data.

Abstract

We calculated the nuclear spin-lattice relaxation rate $1/T_1$ for the D+iD superconducting state with impurities. We found that small amount of unitary impurities quickly produces the residual density of states inside the gap. As a result, the T-linear behavior in 1/T$_1$ is observed at low temperatures. Our results show that the D+iD pairing symmetry of the superconducting state of Na$_{0.35}$CoO$_{2} \cdot y$H$_2$ O is compatible with recent $^{59}$Co 1/T$_1$ experiments of several groups.