Critical magnetic field H c2 and electron scattering in MgB2

Abstract

The correlation between the upper critical field Hc2 and the residual resistivity ρ of the MgB2 compound is studied in a wide range of ρ values. The slope −dHc2/dT of the temperature dependence of Hc2 near Tc is found to increase steadily with increasing residual resistivity to 100 μΩ cm. Over the range from 0 to 50 μΩ cm, the dependence of −dHc2/dT on ρ is fitted well by a linear function, which is typical of a single-band superconductor. The fit is performed using the electronic parameters of the two bands (π and σ) that form the Fermi surface. The field Hc2 is assumed to depend on the electronic parameters of the σ band only. Using this approximation, the following quantities are estimated: the relative contribution of σ electrons to the total conductivity along the boron planes (which turns out to be about 1/2), the ratio of the mean free paths of electrons in the σ and π bands lσ/lπ ≈ 1.5, and the ratios between some other parameters describing electron scattering.