Hump structure below Tc in the thermal conductivity of MgB2 superconductor

A reasonable cause of absence of hump structure in thermal conductivity of MgB2 below the superconducting transition temperature (Tc) lies in the appearance of multigap structure. The gaps of lower magnitude can be suppressed by defects so that this system becomes effectively a single-gap superconductor. When such a situation is created, it is hoped that thermal conductivity (κ) will show hump below Tc. Proceeding along these lines, a sample of MgB2 with a relatively higher residual resistivity ρo = 33.8 μΩ cm has been found to show a hump structure below Tc. The actual electronic thermal conductivity κel of this sample is less than that expected from the Wiedeman–Franz law by more than a factor of 2.6 in the considered temperature range.Modifying the Wiedeman–Franz law for the electronic contribution by replacing the Lorenz number L0 = 2.45 × 10−8 W Ω K−2 by an effective Lorenz number Leff (