Determination of the Upper Critical Field of a Single Crystal LiFeAs: The Magnetic Torque Study up to 35 Tesla

TL;DR

This study measures the upper critical magnetic field of LiFeAs single crystals up to 35 Tesla, revealing anisotropic superconductivity with decreasing anisotropy at low temperatures and evidence of spin-paramagnetic effects.

Contribution

The paper provides the first detailed high-field measurements of B_c2 in LiFeAs, showing its temperature dependence and anisotropy reduction, advancing understanding of its superconducting properties.

Findings

B_c2(0.3K) is 26.4 T for B||ab and 15.5 T for B||c.

Anisotropy parameter Γ decreases from 3 near T_c to 1.7 at low temperatures.

Spin-paramagnetic effects influence B_c2 for B||ab.

Abstract

We report on the upper critical field B_c2 of a superconducting LiFeAs single crystal with T_c~16 K, determined from magnetic torque measurements in dc-magnetic fields up to 35 T and at temperatures down to 0.3 K. B_c2 at 0.3 K is obtained to be 26.4 T and 15.5 T for the applied field B_a||ab and B_a||c, respectively. The anisotropy parameter $\Gamma$=$B_c2^ab / B_c2^c$ is ~ 3 at T_c and decreases to 1.7 as $T \rightarrow 0$, showing rather isotropic superconductivity. While B_c2 is orbitally-limited for B_a||c, the spin-paramagnetic effect is evident in the temperature dependence of B_c2 for B_a||ab