Thermodynamic and Transport Measurements of SuperconductingNa0.3CoO2·1.3H2OSingle Crystals Prepared by Electrochemical Deintercalation

Superconducting single crystal samples of ${\mathrm{Na}}_{0.3}{\mathrm{CoO}}_2·1.3{\mathrm{H}}_2\mathrm{O}$ have been produced using an electrochemical technique which dispenses with the usual bromine chemical deintercalation method. In fully hydrated crystals, susceptibility and specific heat measurements confirm that bulk superconductivity has been achieved. The extracted normal state density of states indicates Fermi-liquid behavior with strong mass enhancement and a modest Wilson ratio. Measurements of $H_{c2}$ for $H\parallel c$ and $H\parallel ab$ reveal significant anisotropy, and the extracted value for the coherence length is about 100 Å, consistent with an extremely narrow bandwidth.