O2 Annealing Induced Superconductivity in FeTe1−x Se x : on the Origin of Superconductivity in FeTe Films

FeTe1−x Se x with x = 0 ∼ 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 O2-annealed samples with x = 0.05 showed superconductivity. The as-grown samples with x = 0.07 ∼ 0.09 also showed no superconductivity but became filamentary superconducting after the O2 annealing. Significant enhancement of bulk superconductivity was achieved for the O2-annealed FeTe1−xSe x with x = 0.11. X-ray photoelectron spectroscopy measurements illustrated that the change of the chemical valence of the elements before and after the O2 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 O2 annealing. These results may clarify the existing debate on the origin of the superconductivity in FeTe thin film.