Upper Critical Field and Kondo Effects in Fe(Te0.9Se0.1) Thin Films by Pulsed Field Measurements

TL;DR

This study investigates the upper critical magnetic field and Kondo effects in Fe(Te0.9Se0.1) thin films, revealing high critical fields and strong magnetoresistance linked to Kondo localization, using pulsed field measurements.

Contribution

It provides the first detailed measurement of the upper critical field in Fe(Te0.9Se0.1) thin films and explores the role of Kondo effects in their superconducting properties.

Findings

Upper critical field Bc2(0) ~ 45 T in thin films

Strong magnetoresistance above Bc2(T) linked to Kondo effects

Kondo localization influences superconducting behavior

Abstract

The transition temperatures of epitaxial films of Fe(Te0:9Se0:1) are remarkably insensitive to applied magnetic field, leading to predictions of upper critical fields Bc2(T = 0) in excess of 100 T. Using pulsed magnetic fields, we find Bc2(0) to be on the order of 45 T, similar to values in bulk material and still in excess of the paramagnetic limit. The same films show strong magnetoresistance in fields above Bc2(T), consistent with the observed Kondo minimum seen above Tc. Fits to the temperature dependence in the context of the WHH model, using the experimental value of the Maki parameter, require an effective spin-orbit relaxation parameter of order unity. We suggest that Kondo localization plays a similar role to spin-orbit pair breaking in making WHH fits to the data.