Superconductivity in a layered cobalt oxyhydrate Na$_{0.31}$CoO$_{2}\cdot$1.3H$_{2}$O

TL;DR

This study confirms bulk superconductivity at 4.3 K in a layered cobalt oxyhydrate, revealing weak-coupled, type-II behavior with point nodes in the gap, and highlights the material's intrinsic two-dimensionality affecting superconducting fraction.

Contribution

First comprehensive electrical, magnetic, and thermal characterization of Na$_{0.31}$CoO$_{2}ullet$1.3H$_{2}$O demonstrating its superconducting properties and gap structure.

Findings

Superconductivity at 4.3 K confirmed in the compound.

Weak-coupled, type-II superconductivity observed.

Point nodes suggested in the superconducting gap.

Abstract

We report the electrical, magnetic and thermal measurements on a layered cobalt oxyhydrate Na$_{0.31}$CoO$_{2}\cdot$1.3H$_{2}$O. Bulk superconductivity at 4.3 K has been confirmed, however, the measured superconducting fraction is relatively low probably due to the sample's intrinsic two-dimensional characteristic. The compound exhibits weak-coupled and extreme type-II superconductivity with the average energy gap $\Delta_{a}(0)$ and the Ginzburg-Landau parameter $\kappa$ of $\sim$ 0.50 meV and $\sim$ 140, respectively. The normalized electronic specific heat data in the superconducting state well fit the $T^{3}$ dependence, suggesting point nodes for the superconducting gap structure.