Possibility of superconductivity in graphite intercalated with alkaline earths investigated with density functional theory

Matteo Calandra; Francesco Mauri

doi:10.1103/PhysRevB.74.094507

paper

Possibility of superconductivity in graphite intercalated with alkaline earths investigated with density functional theory

arXiv:cond-mat/0606372 · doi:10.1103/PhysRevB.74.094507

Abstract

Using density functional theory we investigate the occurrence of superconductivity in AC $_{6}$ with A=Mg,Ca,Sr,Ba. We predict that at zero pressure, Ba and Sr should be superconducting with critical temperatures (T $_{c}$ ) 0.2 K and 3.0 K, respectively. We study the pressure dependence of T $_{c}$ assuming the same symmetry for the crystal structures at zero and finite pressures. We find that the SrC $_{6}$ and BaC $_{6}$ critical temperatures should be substantially enhanced by pressure. On the contrary, for CaC $_{6}$ we find that in the 0 to 5 GPa region, T $_{c}$ weakly increases with pressure. The increase is much smaller than what shown in several recent experiments. Thus we suggest that in CaC $_{6}$ a continous phase transformation, such as an increase in staging, occurs at finite pressure. Finally we argue that, although MgC $_{6}$ is unstable, the synthesis of intercalated systems of the kind Mg $_{x}$ Ca $_{1 - x}$ C $_{y}$ could lead to higher critical temperatures.

9 pages