Thermopower and thermal conductivity of superconducting perovskite $MgCN{i}_3$

Abstract

The thermopower and thermal conductivity of superconducting perovskite $MgCN{i}_3$ ($T_c\approx$ 8 K) have been studied. The thermopower is negative from room temperature to 10 K. Combining with the negative Hall coefficient reported previously, the negative thermopower definetly indicates that the carrier in $MgCN{i}_3$ is electron-type. The nonlinear temperature dependence of thermopower below 150 K is explained by the electron-phonon interaction renormalization effects. The thermal conductivity is of the order for intermetallics, larger than that of borocarbides and smaller than $Mg{B}_2$. In the normal state, the electronic contribution to the total thermal conductivity is slightly larger than the lattice contribution. The transverse magnetoresistance of $MgCN{i}_3$ is also measured. It is found that the classical Kohler's rule is valid above 50 K. An electronic crossover occures at $T^{\ast }\sim 50K$, resulting in the abnormal behavior of resistivity, thermopower, and magnetoresistance below 50 K.

Revised on 12 September 2001, Phys. Rev. B in press