Upward curvature of the upper critical field in the Boson--Fermion model

TL;DR

This paper demonstrates that the Boson-Fermion model accurately reproduces the unconventional upward curvature and non-saturation of the upper critical field in high-$T_c$ superconductors, aligning well with experimental data.

Contribution

It shows that the Boson-Fermion model can explain key features of the upper critical field in high-$T_c$ superconductors, including overdoped compounds.

Findings

$H_{c2}(T)$ exhibits upward curvature at low temperatures.

The model fits experimental $H_{c2}(T)$ data well.

Overdoped compounds are also well described by the model.

Abstract

We report on a non-conventional temperature behavior of the upper critical field ($H_{c2}(T)$) which is found for the Boson-Fermion (BF) model. We show that the BF model properly reproduces two crucial features of the experimental data obtained for high-$T_c$ superconductors: $H_{c2}(T)$ does not saturate at low temperatures and has an upward curvature. Moreover, the calculated upper critical field fits very well the experimental results. This agreement holds also for overdoped compounds, where a purely bosonic approach is not applicable.