Upper critical field in the model with finite range interaction between electrons

TL;DR

This paper develops a theory for the upper critical magnetic field in superconductors with nonlocal electron interactions, predicting enhanced critical fields and specific temperature behaviors influenced by impurity scattering.

Contribution

It introduces a model incorporating finite-range electron interactions and analyzes their effects on the upper critical field in superconductors.

Findings

Nonlocal interaction characterized by $k_F ho_0$ influences $H_{c2}$.

External magnetic field induces additional order parameter components.

Impurity scattering suppresses nonlocal effects in the dirty limit.

Abstract

We develop a theory of the upper critical field in a BCS superconductor with a nonlocal interaction between electrons. We have shown that the nonlocal interaction is characterized by the parameter $k_F\rho_0$ where $k_F$ is the Fermi momentum and $\rho_0$ is the radius of electron-electron interaction. The presence of the external magnetic field leads to the generation of additional components of the order parameter with different angular momentum. This effect leads to the enhancement of the upper critical field above the orbital limiting field. In addition the upward curvature in the temperature dependence of $H_{c2}(T)$ in the clean limit is predicted. The impurity scattering suppresses the effect in the dirty limit.