Unusual persistence of superconductivity against high magnetic fields in the strongly-correlated iron-chalcogenide film FeTe:O$_{x}$

TL;DR

This study reveals an unusual persistence of superconductivity in FeTe:O$_{x}$ films under high magnetic fields, indicating complex superconducting states and challenging conventional theories in strongly-correlated iron-based superconductors.

Contribution

It demonstrates the existence of finite-momentum superconducting states in FeTe:O$_{x}$, expanding understanding of superconductivity in strongly-correlated materials.

Findings

Superconductivity persists against high magnetic fields below ~2.5 K.

Upper critical field increases with decreasing temperature, contrary to mean-field expectations.

Finite-momentum superconducting states can exist within conventional theory despite its limitations.

Abstract

We report an unusual persistence of superconductivity against high magnetic fields in the iron chalcogenide film FeTe:O$_{x}$ below ~ 2.5 K. Instead of saturating like a mean-field behavior with a single order parameter, the measured low-temperature upper critical field increases progressively, suggesting a large supply of superconducting states accessible via magnetic field or low-energy thermal fluctuations. We demonstrate that superconducting states of finite momenta can be realized within the conventional theory, despite its questionable applicability. Our findings reveal a fundamental characteristic of superconductivity and electronic structure in the strongly-correlated iron-based superconductors.