Critical Field of Al-Doped MgB2 Samples: Correlation with the Suppression of Sigma-Band Gap
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, Deltasigma, 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 Deltasigma. For larger doping we observed the crossover to the dirty regime driven mostly by the strong decrease of Deltasigma rather than by the increase of the sigma-band scattering rate
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