Observation of two-level critical state in the superconducting FeTe thin films

TL;DR

This study investigates the superconducting properties of FeTe thin films, revealing a two-level critical state and granularity effects that influence their magnetic hysteresis and superfluid density.

Contribution

It introduces the observation of a two-level critical state in FeTe thin films, highlighting the role of granularity in their superconductivity, which was not previously understood.

Findings

High Tc films exhibit non-saturating superfluid density

Magnetic hysteresis indicates a two-level critical state

Granularity significantly affects superconducting behavior

Abstract

FeTe, a non-superconducting parent compound in the iron-chalcogenide family, becomes superconducting after annealing in oxygen. Under the presence of magnetism, spin-orbit coupling, inhomogeneity and lattice distortion, the nature of its superconductivity is not well understood. Here, we combined mutual inductance technique with magneto transport to study the magnetization and superconductivity of FeTe thin films. We found that the films with the highest Tc showed non-saturating superfluid density and a strong magnetic hysteresis distinct from that in a homogeneous superconductor. Such hysteresis can be well explained by a two-level critical state model and suggested the importance of granularity to superconductivity in this compound.