Reversible Tuning of Magnetic Order and Intrinsic Superconductivity in Strained FeTe Films via Stoichiometry Control.

FeTe is a prototypical parent compound of iron-based superconductors. While bulk FeTe is nonsuperconducting with a long-range bicollinear antiferromagnetic order, superconductivity has been achieved in thin films. However, the approaches usually involve complex oxygen incorporation or interfacial effects, the microscopic mechanisms of which remain elusive. Here, we prepare high-purity, bare FeTe thin films on SrTiO using molecular beam epitaxy and investigate their magnetic and superconducting states combining both microscopic and macroscopic characterizations. By reducing the interstitial Fe impurities, we successfully suppress the long-range antiferromagnetic order, enhance the quasiparticle coherence, reduce electron doping and induce superconductivity at above 10 K simultaneously. Moreover, this process is readily reversible by tuning the Fe concentration through well-controlled annealing treatments. Theoretical calculations suggest a spin-fluctuated magnetic ground state under tensile strain. Our findings reveal that strained FeTe thin film is intrinsically superconducting and the precise stoichiometry is a key prerequisite. This work provides insights into the competition between magnetism and superconductivity in iron chalcogenides, and supplies methods for developing stable, high-purity superconducting FeTe films.