Competing effects of mass anisotropy and spin Zeeman coupling on the upper critical field of a mixed $d$- and s-wave superconductor

TL;DR

This paper investigates how mass anisotropy and spin Zeeman coupling influence the upper critical field in mixed d- and s-wave superconductors, revealing their opposing effects and aligning theory with experimental data.

Contribution

It provides a microscopic analysis of the competing effects of mass anisotropy and spin Zeeman coupling on the upper critical field in mixed superconductors.

Findings

Mass anisotropy enhances $H_{c2}$.

Zeeman coupling suppresses $H_{c2}$.

$H_{c2}$ saturates at zero temperature.

Abstract

Based on the linearized Eilenberger equations, the upper critical field $(H_{c2})$ of mixed d- and s-wave superconductors has been microscopically studied with an emphasis on the competing effects of mass anisotropy and spin Zeeman coupling. We find the mass anisotropy always enhance $H_{c2}$ while the Zeeman interaction suppresses $H_{c2}$. As required by the thermodynamics, we find $H_{c2}$ is saturated at zero temperature. We compare the theoretical calculations with recent experimental data of YBa$_{2}$Cu$_{3}$O$_{7-+AFw-delta}$.