Entropy and Spin Susceptibility of s-wave Type-II Superconductors near $H_{c2}$

TL;DR

This theoretical study analyzes entropy and spin susceptibility near the upper critical field in s-wave type-II superconductors, revealing how impurity levels affect their behavior and deviations from linearity.

Contribution

It provides a quantitative analysis of entropy and spin susceptibility near $H_{c2}$, highlighting impurity-dependent behaviors and their relation to flux-flow resistivity.

Findings

Slopes $oldsymbol{ ext{α}_S}$ and $oldsymbol{ ext{α}_χ}$ at T=0 are identical.

These slopes vary from 1.72 in the dirty limit to 0.5-0.6 in the clean limit.

Entropy and susceptibility near T=0 deviate from linear behavior depending on impurity levels.

Abstract

A theoretical study is performed on the entropy $S_{\rm s}$ and the spin susceptibility $\chi_{\rm s}$ near the upper critical field $H_{c2}$ of s-wave type-II superconductors with arbitrary impurity concentrations. The changes of these quantities through $H_{c2}$ may be expressed as $[S_{\rm s}(T,B)-S_{\rm s}(T,0)]/[S_{\rm n}(T)-S_{\rm s}(T,0)]=1-\alpha_{S}(1-B/H_{c2})\approx (B/H_{c2})^{\alpha_{S}}$, for example, where $B$ is the average flux density and $S_{\rm n}$ denotes entropy in the normal state. It is found that the slopes $\alpha_{S}$ and $\alpha_{\chi}$ at T=0 are identical, connected directly with the zero-energy density of states, and vary from 1.72 in the dirty limit to $0.5\sim 0.6$ in the clean limit. This mean-free-path dependence of $\alpha_{S}$ and $\alpha_{\chi}$ at T=0 is quantitatively the same as that of the slope $\alpha_{\rho}(T=0)$ for the flux-flow resistivity studied previously. The result suggests that $S_{\rm s}(B)$ and $\chi_{\rm s}(B)$ near T=0 are convex downward (upward) in the dirty (clean) limit, deviating substantially from the linear behavior $\propto B/H_{c2}$. The specific-heat jump at $H_{c2}$ also shows fairly large mean-free-path dependence.