Superconductivity in Ce-based cage compounds

TL;DR

This paper investigates the emergence of nodal d-wave superconductivity in Ce-based cage compounds CeNi$_2$Cd$_{20}$ and CePd$_2$Cd$_{20}$, proposing that valence fluctuations and pressure can enhance their superconducting transition temperature.

Contribution

It introduces an extended periodic Anderson model including Coulomb interactions to explain superconductivity mediated by valence fluctuations in these compounds.

Findings

Superconductivity is likely mediated by valence fluctuations in these compounds.

Applying hydrostatic pressure can significantly increase the critical temperature.

Fluctuations lead to the emergence of d-wave superconductivity.

Abstract

Cerium-based ternary compounds CeNi$_2$Cd$_{20}$ and CePd$_2$Cd$_{20}$ do not exhibit long-range order down to millikelvin temperature range. Given the large separation between cerium ions which significantly reduces the superexchange interactions and vanishingly small RKKY 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 of d-wave superconductivity.