Anisotropic, Fermi-Surface-Induced Variation in Tc in MgB2 Alloys
Abstract
Using coherent-potential to describe disorder, Gaspari-Gyorffy approach to evaluate electron-phonon coupling, and Allen-Dynes equation to calculate Tc, we show that in Mg1-xMxB2 (M = Al,Li or Zn) alloys (i) the way Tc changes depends on the location of the added/modified k-resolved states on the Fermi surface and (ii) the variation of Tc as a function of concentration is dictated by the B p DOS. In addition, using full-potential calculations for MgMB4, we show that (i) at x=0.5 a superstructure can form in Mg1-xAlxB2 but not in Mg1-xLixB2 or Mg1-xZnxB2, and (ii) B layer shifts towards the impurity layer, more for Al than for Li or Zn.
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