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Superconductivity in two-dimensional CoO2 layers


Since the discovery of high-transition-temperature (high-Tc) superconductivity in layered copper oxides1, many researchers have searched for similar behaviour in other layered metal oxides involving 3d-transition metals, such as cobalt and nickel. Such attempts have so far failed, with the result that the copper oxide layer is thought to be essential for superconductivity. Here we report that NaxCoO2·yH2O (x ≈ 0.35, y ≈ 1.3) is a superconductor with a Tc of about 5 K. This compound consists of two-dimensional CoO2 layers separated by a thick insulating layer of Na+ ions and H2O molecules. There is a marked resemblance in superconducting properties between the present material and high-Tc copper oxides, suggesting that the two systems have similar underlying physics.

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Figure 1: Structural views of Na0.7CoO2 (left) and NaxCoO2·yH2O (right), where Na and H2O sites are partially occupied.
Figure 2: Rietveld refinement patterns for NaxCoO2·yH2O.
Figure 3: Magnetic susceptibility (χ) of NaxCoO2·yH2O.
Figure 4: Resistivity (ρ) of NaxCoO2·yH2O under zero magnetic field.


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We thank Y. Yajima, S. Takenouchi and H. Komori of our institute for IR, ICP-AES and EDX analysis.

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Correspondence to Kazunori Takada.

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The authors declare that they have no competing financial interests.

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Takada, K., Sakurai, H., Takayama-Muromachi, E. et al. Superconductivity in two-dimensional CoO2 layers. Nature 422, 53–55 (2003).

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