Heat and charge transport properties of MgB2

A polycrystalline sample of the MgB2 superconductor was investigated by mea surements of the electrical resistivity, the thermopower and the thermal co nductivity 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. Th e electron diffusion thermopower and its band-structure-derived value indic ate the dominant hole character of the charge carriers. The total thermopow er can be explained by the diffusion term renormalized by a significant ele ctron-phonon interaction and a phonon drag term. In the thermal conductivit y, 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 beh aviour of non-magnetic borocarbides. (C) 2001 Elsevier Science B.V. All rig hts reserved.