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Thermodynamic and Transport Measurements on Superconducting Na_xCoO_2 + yH_2O Single Crystals Prepared by Electrochemical De-intercalation

F. C. Chou·J. H. Cho·Patrick A. Lee·E. T. Abel·K. Matan·Young S. Lee
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Abstract

Superconducting single crystal samples of Na_xCoO_2 + yH_2O have been produced using an electrochemical technique which dispenses with the usual bromine chemical de-intercalation step and permits much more precise control of the Na content. After careful hydration, nearly single-phase crystals have been obtained in which over 90% of the sample's volume corresponds to the superconducting Na_{0.3}CoO_2 + 1.3H_2O structure. 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||c and H||ab reveal significant anisotropy. The estimated value of H_{c2} for H||c yields a coherence length of ~100 A, consistent with an extremely narrow bandwidth.

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F. C. Chou, J. H. Cho, Patrick A. Lee, E. T. Abel, K. Matan, Young S. Lee. 2003-10-17. Thermodynamic and Transport Measurements on Superconducting Na_xCoO_2 + yH_2O Single Crystals Prepared by Electrochemical De-intercalation. https://doi.org/10.1103/physrevlett.92.157004

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