Stoichiometric FeTe is a superconductor

Iron-based superconductors (FeSCs) are a fascinating family of materials in which several electronic bands and strong antiferromagnetic (AFM) correlations are key ingredients for competing ground states^1-6, including antiferromagnetism, electronic nematicity and unconventional superconductivity. FeTe, unlike its superconducting isostructural counterpart FeSe, has long been considered an AFM metal sans superconductivity^7-9. Here we use molecular-beam epitaxy (MBE) to grow FeTe films and perform post-growth annealing under a Te flux. By performing spin-polarized scanning tunnelling microscopy and spectroscopy (STM/S), we demonstrate that the AFM order in as-grown FeTe films is induced by interstitial Fe atoms that disrupt the ideal 1:1 stoichiometry. Notably, 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 about 13.5 K. This superconducting state is further confirmed by the observation of Cooper-pair tunnelling, 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^10-15 and demonstrates the importance of stoichiometry control in understanding the competition between antiferromagnetism and superconductivity in FeSCs.