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Solid State Sciences
Volume 12, Issue 5, May 2010, Pages 656-659
International Symposium on Structure-Property Relationships in Solid-State Materials













doi:10.1016/j.solidstatesciences.2008.09.016 | How to Cite or Link Using DOI
Copyright © 2008 Elsevier Masson SAS All rights reserved.
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Superconducting transition temperature and the thickness of CoO2 planes of NaxCoO2·yH2O





Taketo Moyoshia, Yoshiaki Kobayashia, Yukio Yasuia, Masatoshi Satoa, Corresponding Author Contact Information, E-mail The Corresponding Author and Kazuhisa Kakuraib






a Department of Physics, Division of Material Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan


b Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki 319-1195, Japan





Received 7 July 2008; 


revised 29 September 2008; 


accepted 29 September 2008. 


Available online 10 October 2008.







Abstract


The superconductivity of NaxCoO2·yH2O appears in two regions of νQ divided by a narrow nonsuperconducting phase in the TcνQ phase diagram, where Tc and νQ are the superconducting transition temperature and 59Co-nuclear quadrupole frequency, respectively. It suggests that the existence/nonexistence of the superconductivity depends on the local structure around Co sites or on the thickness of the CoO2 planes, through the change of the crystal field. We have carried out specific heat measurements on several samples with different νQ values distributing over both the superconducting νQ regions, and found that the electronic specific heat coefficient γ does not change significantly with νQ. It suggests that a topological change of the Fermi surface which has been proposed as a possible origin of the existence of the two superconducting regions, does not take place with the change of the local structure around Co sites or thickness of the CoO2 planes. We have also carried out neutron inelastic measurements on aligned crystals of NaxCoO2·yD2O, and found that ferromagnetic fluctuations with two-dimensional character observed in the high temperature region lose their intensities with decreasing T and becomes inappreciable below 25 K. It indicates that the hole-pockets near the K points in the reciprocal space do not exist in these crystals. Combining these results, we can exclude, in the entire region of νQ, the existence of the hole-pockets, on which arguments of the possible triplet superconductivity are based. The present results are consistent with the singlet pairing which we showed in previous papers.







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Keywords: NaxCoO2·yH2O; Specific heat; Fermi surface topology; Neutron scattering; Magnetic excitation





Article Outline



1. Introduction
2. Experimental
3. Results and discussion
4. Summary
Acknowledgements
References































Corresponding author. Tel.: +81 52 789 3537; fax: +81 52 789 2856.












Solid State Sciences
Volume 12, Issue 5, May 2010, Pages 656-659
International Symposium on Structure-Property Relationships in Solid-State Materials




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  • Chen Wev .  honorary member of ISSC science council

  • Harton Vladislav Vadim  honorary member of ISSC science council

  • Lichtenstain Alexandr Iosif  honorary member of ISSC science council

  • Novikov Dimirtii Leonid  honorary member of ISSC science council

  • Yakushev Mikhail Vasilii  honorary member of ISSC science council

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