Heat and charge transport properties of MgB 2

Abstract

A polycrystalline sample of the MgB 2 superconductor was investigated by measurements of the electrical resistivity, the thermopower and the thermal conductivity in the temperature range between 1.8 and 300 K in zero magnetic field. The electrical resistivity shows a superconducting transition at T c=38.7 K and, similarly to borocarbides, a T 2.4 behaviour up to 200 K. The electron diffusion thermopower and its band-structure-derived value indicate the dominant hole character of the charge carriers. The total thermopower can be explained by the diffusion term renormalized by a significant electron–phonon interaction and a phonon drag term. In the thermal conductivity, for decreasing temperature, a significant decrease below T c is observed resulting in a T 3 behaviour below 7 K. The reduced Lorenz number exhibits values smaller than 1 and a characteristic minimum which resembles the behaviour of non-magnetic borocarbides.