O2 Annealing Induced Superconductivity in FeTe1-xSex: on the Origin of Superconductivity in FeTe Films

FeTe1-xSex with x = 0 similar to 0.13 polycrystalline samples was fabricated by solid-state reaction and annealed in oxygen. The magnetic and transport measurements illustrated that neither the as-grown nor the O-2-annealed samples with x = 0.05 showed superconductivity. The as-grown samples with x = 0.07 similar to 0.09 also showed no superconductivity but became filamentary superconducting after the O-2 annealing. Significant enhancement of bulk superconductivity was achieved for the O-2-annealed FeTe1-xSex with x = 0.11. X-ray photoelectron spectroscopy measurements illustrated that the change of the chemical valence of the elements before and after the O-2 annealing was not the main factor responsible for the occurrence of superconductivity. The superconducting transition was mainly caused by the suppression of antiferromagnetic ordering, due to the lattice shrinkage induced by the O-2 annealing. These results may clarify the existing debate on the origin of the superconductivity in FeTe thin film.