Superconducting Properties under Magnetic Field in Na$_{0.35}$CoO$_{2}{\cdot}1.3$H$_{2}$O Single Crystal

TL;DR

This study investigates the superconducting properties of Na$_{0.35}$CoO$_{2}{ imes}1.3$H$_{2}$O single crystals, revealing their anisotropic three-dimensional nature and potential spin singlet pairing through resistivity and magnetic susceptibility measurements.

Contribution

The paper provides detailed measurements of the upper critical field and coherence length, demonstrating the anisotropic superconductivity and possible Pauli limit suppression in this material.

Findings

Superconducting transition temperature $T_c$ is 4.5 K.

Anisotropy ratio of coherence lengths is approximately 9.2.

Upper critical field $H_{c2}$ is suppressed to the Pauli limit in the ab-plane.

Abstract

We report the in-plane resistivity and magnetic susceptibility of the layered cobalt oxide Na$_{0.35}$CoO$_{2}{\cdot}1.3$H$_{2}$O single crystal. The temperature dependence of the resistivity shows metallic behavior from room temperature to the superconducting transition temperature $T_{c}$ of 4.5 K. Sharp resistive transition, zero resistivity and almost perfect superconducting volume fraction below $T_{c}$ indicate the good quality and the bulk superconductivity of the single crystal. The upper critical field $H_{c2}$ and the coherence length $\xi$ are obtained from the resistive transitions in magnetic field parallel to the c-axis and the $ab$-plane. The anisotropy of $\xi$, $\xi_{ab} / \xi_{c} =$ 12 nm/1.3 nm $\simeq$ 9.2, suggests that this material is considered to be an anisotropic three dimensional superconductor. In the field parallel to the $ab$-plane, $H_{c2}$ seems to be suppressed to the value of Pauli paramagnetic limit. It may indicate the spin singlet superconductivity in the cobalt oxide.