Unconventional superconductivity in Na$_{0.35}$CoO$_{2}\cdot$1.3D$_{2}$O and proximity to a magnetically ordered phase

TL;DR

This study reveals unconventional superconductivity in Na$_{0.35}$CoO$_{2}ullet$1.3H$_{2}$O, characterized by high effective mass, anisotropic pairing, and proximity to magnetic order, using muon spin relaxation measurements.

Contribution

It provides new insights into the unconventional nature of superconductivity in layered cobalt oxides and their relation to magnetic phases, using $ m{ extmu}$SR techniques.

Findings

High effective mass of charge carriers (~100 times electron mass)

Superconducting $T_c$ scales with superfluid energy similar to cuprates

Superconductivity exhibits anisotropic pairing without time-reversal symmetry breaking

Abstract

Muon spin relaxation ($\mu$SR) measurements on the new layered cobalt oxide superconductor Na$_{0.35}$CoO$_{2}\cdot$1.3H$_{2}$O and its parent, non-superconducting compounds, have revealed unconventional nature of superconductivity through: (1) a small superfluid energy which implies a surprisingly high effective mass of the charge carriers, approximately 100 times the bare electron mass; (2) the superconducting transition temperature $T_{c}$ scaling with the superfluid energy following the correlations found in high-$T_{c}$ cuprate and some other two-dimensional superconductors; (3) an anisotropic pairing without broken time-reversal symmetry; and (4) the proximity of a magnetically ordered insulating phase at Na$_{0.5}$CoO$_{2}$ below $T_{N}$ = 53 K.