Enhancement of superconductivity and evidence of structural instability in intercalated graphite CaC6 under high pressure |
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Authors: | Gauzzi A Takashima S Takeshita N Terakura C Takagi H Emery N Hérold C Lagrange P Loupias G |
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Institution: | Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8581, Japan. |
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Abstract: | We measured the temperature dependent resistivity, varrho(T), of the intercalated graphite superconductor CaC6 as a function of pressure up to 16 GPa. We found a large linear increase of critical temperature, Tc, from the ambient pressure value 11.5 K up to 15.1 K, the largest value for intercalated graphite, at 7.5 GPa. At approximately 8 GPa, a jump of varrho and a sudden drop of Tc down to approximately 5 K indicates the occurrence of a phase transition. Our data analysis suggests that a pressure-induced phonon softening related to an in-plane Ca phonon mode is responsible for the Tc increase and that higher pressures greater, similar8 GPa lead to a structural transition into a new phase with a low Tc less, similar3 K. |
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