The upper critical field and its anisotropy in LiFeAs

TL;DR

This study measures the upper critical magnetic field of LiFeAs single crystals, revealing moderate anisotropy and lower critical field values compared to other iron-based superconductors, with behavior explained by the WHH model.

Contribution

It provides the first detailed measurement of the anisotropic upper critical field in LiFeAs, showing its temperature dependence and limiting mechanisms.

Findings

Anisotropy parameter γ approaches 1.5 at low temperatures.

Upper critical fields are 15T (c-axis) and 24.2T (ab-plane) at 1.4K.

Critical fields are lower than in other iron-based superconductors.

Abstract

The upper critical field $\mu_0H_{c2}(T_c)$ of LiFeAs single crystals has been determined by measuring the electrical resistivity using the facilities of pulsed magnetic field at Los Alamos. We found that $\mu_0H_{c2}(T_c)$ of LiFeAs shows a moderate anisotropy among the layered iron-based superconductors; its anisotropic parameter $\gamma$ monotonically decreases with decreasing temperature and approaches $\gamma\simeq 1.5$ as $T\rightarrow 0$. The upper critical field reaches 15T ($H\parallel c$) and 24.2T ($H\parallel ab$) at $T=$1.4K, which value is much smaller than other iron-based high $T_c$ superconductors. The temperature dependence of $\mu_0H_{c2}(T_c)$ can be described by the Werthamer-Helfand-Hohenberg (WHH) method, showing orbitally and (likely) spin-paramagnetically limited upper critical field for $H\parallel c$ and $H\parallel ab$, respectively.