Enhancement of Superconductivity and Evidence of Structural Instability in Intercalated Graphite CaC6 under High Pressure
A. Gauzzi, S. Takashima, N. Takeshita, C. Terakura, H. Takagi, N. Emery, C. Hérold, P. Lagrange, G. Loupias
DOI 10.1103/PhysRevLett.98.067002 · Physical Review Letters
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Abstract
We measured the temperature dependent resistivity, ϱ(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 ≈8 GPa, a jump of ϱ and a sudden drop of Tc down to ≈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 ≳8 GPa lead to a structural transition into a new phase with a low Tc≲3 K.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| CaC6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 11.5 | Pressure unresolved | onset |
| CaC6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 11.2 | Pressure unresolved | zero_resistance |
| CaC6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 15.1 | 7.5 GPa | onset |
| CaC6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 5 | 8 GPa | onset |
| MgB6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 39 | Pressure not reported | unknown |
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