paper

Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors

arXiv:cond-mat/0212129 · doi:10.1103/PhysRevB.67.184515

Abstract

Quasiclassic Uzadel equations for two-band superconductors in the dirty limit with the account of both intraband and interband scattering by nonmagnetic impurities are derived for any anisotropic Fermi surface. From these equations the Ginzburg-Landau equations, and the critical temperature are obtained. An equation for the upper critical field, which determines both the temperature dependence of and the orientational dependence of as a function of the angle between and the c-axis is obtained. It is shown that the shape of the curve essentially depends on the ratio of the intraband electron diffusivities and , and can be very different from the standard one-gap dirty limit theory. In particular, the value can considerably exceed , which can have important consequences for applications of . A scaling relation is proposed which enables one to obtain the angular dependence of from the equation for at . It is shown that, depending on the relation between and , the ratio of the upper critical field for and can both increase and decrease as the temperature decreases. Implications of the obtained results for are discussed.

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