Critical magnetic field Hc2 and electron scattering in MgB2

The correlation between the upper critical field H-c2 and the residual resistivity rho of the MgB2 compound is studied in a wide range of rho values. The slope -dH(c2)/dT of the temperature dependence of H-c2 near T-c is found to increase steadily with increasing residual resistivity to 100 mu Omega cm. Over the range from 0 to 50 mu Omega cm, the dependence of -dH(c2)/dT on rho 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 (pi and sigma) that form the Fermi surface. The field H-c2 is assumed to depend on the electronic parameters of the sigma band only. Using this approximation, the following quantities are estimated: the relative contribution of sigma 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 sigma and pi bands l (sigma)/l (pi) approximate to 1.5, and the ratios between some other parameters describing electron scattering.