Superconductivity in Ce-based cage compounds

Cerium-based ternary compounds CeNi₂Cd₂₀and CePd₂Cd₂₀do not exhibit long-range order down to millikelvin temperature range. Given the large separation between Ce ions which significantly reduces the super-exchange interactions and vanishingly small Ruderman-Kittel-Kasuya-Yosida interaction, here we show that nodal superconductivity mediated by the valence fluctuations must be a ground state in these materials. We propose that the critical temperature for the superconducting transition can be significantly increased by applying hydrostatic pressure. We employ an extended periodic Anderson lattice model which includes the long-range Coulomb interactions between the itinerant electrons as well as the local Coulomb interaction between the predominantly localized and itinerant electrons to compute a critical temperature of the superconducting transition. Using the slave-boson approach we show that fluctuations mediated by the repulsive electron-electron interactions lead to the emergence ofd-wave superconductivity.