Influence of the nonuniform superconductivity on the upper critical field in the extended saddle-point model

Abstract

The upper critical field is calculated in the framework of the extended saddle-point model, taking into account the formation of a nonuniform superconducting state. The temperature dependence of the upper critical field is characterized by a positive curvature at all temperatures. This peculiar behavior may be of some relevance to the experimental data on low-dimensional superconductors and overdoped ${\mathrm{Tl}}_{2}{\mathrm{Ba}}_{2}{\mathrm{CuO}}_{6}$ single crystals.