Stoichiometric FeTe is a Superconductor

TL;DR

This study shows that stoichiometric FeTe is inherently a superconductor with a critical temperature of about 13.5K, challenging previous beliefs that it is solely an antiferromagnetic metal.

Contribution

The work demonstrates that removing interstitial Fe atoms in FeTe films induces superconductivity, revealing stoichiometric FeTe as a superconductor and clarifying its role in iron-based superconductors.

Findings

Stoichiometric FeTe exhibits superconductivity at ~13.5K.

Interstitial Fe atoms induce antiferromagnetic order in FeTe.

Te annealing removes interstitial Fe, enabling superconductivity.

Abstract

Iron-based superconductors are a fascinating family of materials in which multiple electronic bands and strong antiferromagnetic (AFM) correlations are key ingredients for competing ground states, including antiferromagnetism, electronic nematicity, and unconventional superconductivity. FeTe, unlike its superconducting isostructural counterpart FeSe, has long been regarded as an AFM metal sans superconductivity. In this work, we employ molecular beam epitaxy to grow FeTe films and perform post-growth annealing under a Te flux. By performing spin-polarized scanning tunneling microscopy and spectroscopy, we demonstrate that the AFM order in as-grown FeTe films is induced by interstitial Fe atoms that disrupt the ideal 1:1 stoichiometry. Remarkably, the removal of these interstitial Fe atoms through Te annealing yields stoichiometric FeTe films that show no AFM order and instead exhibit robust superconductivity with a critical temperature of ~13.5K. This superconducting state is further confirmed by the observation of Cooper pair tunneling, zero electrical resistance, and the Meissner effect. Therefore, our results demonstrate that stoichiometric FeTe is inherently a superconductor, overturning a long-held view that it is an AFM metal. This work clarifies the origin of superconductivity in FeTe-based heterostructures and demonstrates the importance of stoichiometry control in understanding the competition between AFM and superconductivity in iron-based superconductors.