Superconductivity in layered nitride with small carrier density

Abstract We have systematically investigated the doping dependence of specific heat and magnetic susceptibility for layer-structured Li x ZrNCl superconductors with small carrier density. It was found that the superconducting pairing interaction strength and the spin susceptibility are concomittantly enhanced in parallel with T c upon decreasing the carrier density, while density of states at the Fermi level shows little doping dependence. A model calculation based on the Hubbard model qualitatively reproduces the enhancement of susceptibility as the band insulator is approached.