Evidence for Anisotropic Vortex Dynamics and Pauli Limitation in the Upper Critical Field of FeSe1-xTex

TL;DR

This study investigates the anisotropic vortex behavior and Pauli limiting effects on the upper critical field of FeSe1-xTex, revealing near isotropic thermodynamic critical fields and the importance of Pauli limiting in this superconductor.

Contribution

It provides new insights into the anisotropic vortex dynamics and the role of Pauli limiting in FeSe1-xTex, combining resistivity, specific heat, and pulsed field measurements.

Findings

Thermodynamic HC2 is nearly isotropic.

Anisotropic vortex dynamics influence resistivity measurements.

Pauli limiting is essential for fitting HC2(T).

Abstract

We have determined HC2(T) for FeSe1-xTex (x=0.52) single crystals using resistivity measurements at high static and pulsed magnetic field, as well as specific heat measurements up to 9T. We find that the significant anisotropy of the initial slope of HC2(T) determined from resistivity measurements, is not present when HC2 is determined from the specific heat results. This suggests that the thermodynamic upper critical field is almost isotropic, and that anisotropic vortex dynamics play a role. Further evidence of anisotropic vortex dynamics is found in the behaviour in pulsed field. We also find that Pauli limiting must be included in order to fit the temperature dependence of HC2, indicating probably higher effective mass in FeSe1-xTex than in other Fe superconductors.