T-3ν_Q Phase Diagram of Hydrated Cobalt Oxides Na_xCoO_2・yH_2O(Condensed matter : electronic structure and electrical, magnetic, and optical properties)

概要

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The superconducting transition temperatures of Na_xCoO_2・yH_2O prepared by various methods have been found to exhibit the systematic dependence on the nuclear quadrupole frequency ν_Q. In the T-3ν_Q phase diagram, the superconducting region of 3ν_Q, spreading over the region between 〜12.0 and 〜12.9MHz, is divided into two regions by the nonsuperconducting phase between 〜12.5 and 〜12.6MHz. We have investigated the origin of the nonsuperconducting phase by detailed measurements of ^<59>Co-NQR and ^2D-NMR, and the results indicate that the nonsuperconducting phase is possibly in the charge-density-wave or the charge disproportionate state, in which the magnetic moments induced inhomogeneously by this transition become frozen at low temperatures.
社団法人日本物理学会の論文
2007-10-15