Critical Field of Al-Doped MgB2 Samples: Correlation with the Suppression of Sigma-Band Gap
arXiv:cond-mat/0406377 · doi:10.1103/PhysRevB.71.144505
Abstract
In this Letter, the study of the effect of Al substitution on the upper critical field, Bc2, in AlxMg1-xB2 samples is presented. We find a straightforward correlation between Bc2 and the sigma-band gap, Delta_sigma, evaluated by point-contact measurements. Up to x=0.2 Bc2 can be well described within a clean limit model and its decrease with x is directly related to the suppression of Delta_sigma. For larger doping we observed the crossover to the dirty regime driven mostly by the strong decrease of Delta_sigma rather than by the increase of the sigma-band scattering rate
5 pages, 4 figures