title: Enhancement of superconductivity and evidence of structural instability in intercalated graphite CaC6 under high pressure.
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.
authors.affiliation: Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Gauzzi
authors.forename: S
authors.initials: S
authors.lastname: Takashima
authors.forename: N
authors.initials: N
authors.lastname: Takeshita
authors.forename: C
authors.initials: C
authors.lastname: Terakura
authors.forename: H
authors.initials: H
authors.lastname: Takagi
authors.forename: N
authors.initials: N
authors.lastname: Emery
authors.forename: C
authors.initials: C
authors.lastname: Hérold
authors.forename: P
authors.initials: P
authors.lastname: Lagrange
authors.forename: G
authors.initials: G
authors.lastname: Loupias