Transport properties of the transition metal superconductors

Abstract

The thermal conductivity coefficient is calculated for a d-band superconductor described by a Hamiltonian which combines a Bardeen-Cooper-Schrieffer-type electron-phonon interaction between the d-electrons of the transition metal with the Anderson Hamiltonian. Since the heat current is carried only by normal s-electrons in both the normal and superconducting phases, the Green’s functions for the s-electrons are used in Kubo’s expression for thermal conductivity. Because of the hybridization term in our Hamiltonian, the s-band electrons also begin to condense into superelectrons which do not carry any heat. Numerical evaluation of thermal conductivity of the d-band superconductor is carried out as a function of temperature. The resulting curve shows the general features of the thermal conductivity behavior seen in superconducting niobium.