Evidence for dominant Pauli paramagnetic effect in the upper critical fields of a FeTe0.6Se0.4 superconductor

TL;DR

This study measures the upper critical fields of FeTe0.6Se0.4 superconductor, revealing a dominant Pauli paramagnetic effect influencing its superconducting properties and critical field behavior.

Contribution

It provides evidence for a dominant Pauli paramagnetic effect in FeTe0.6Se0.4, supported by detailed Hc2(T) measurements and modeling considering spin effects.

Findings

Strong bending in Hc2ab(T) curves indicating Pauli effect

Nearly isotropic Hc2(0) values around 48 T

Werthamer-Helfand-Hohenberg model effectively describes data

Abstract

We investigate temperature-dependence of the upper critical fields Hc2(T) of a superconducting FeTe0.6Se0.4 single crystal by measuring resistivity in static magnetic fields up to 45 T. The observations of strong bending in the Hc2ab(T) curves and nearly isotropic Hc2ab(0) ~ Hc2c(0) ~ 48 T support the presence of strong Pauli paramagnetic effect. We show that the Werthamer-Helfand-Hohenberg formula considering the Pauli limiting and the spin-orbit scattering together can effectively describe both Hc2ab(T) and Hc2c(T) curves. The enhancement in quasi-particle density of states or increased scattering resulting from Te(Se) vacancy or excess Fe is discussed as a possible origin for the manifesting Pauli paramagnetic effect.