Optimal charge inhomogeneity for the d+i d-wave superconductivity in the intercalated graphite CaC 6

The coexistence of superconductivity and charge inhomogeneity was observed in many cuprate superconductors. The relationship between those two is still controversial. Similarly, in the graphene sheets of the intercalated graphitic superconductor CaC 6, the charge inhomogeneity was also observed. We simulate such a system by constructing the Hubbard model on the honeycomb lattice with charge inhomogeneity imposed by force. Utilizing the finite-temperature determinant quantum Monte Carlo algorithm, we examine the relationship between the superconducting pairing and the charge inhomogeneity. An optimal charge inhomogeneity for the d+i d-wave pairing is found. While for other artificial charge inhomogeneities, the d+i d-wave pairing is monotonically suppressed. The possible π-phase shift induced by charge inhomogeneity is also examined.