Superconductivity in Fe$_{1.08}$Te:O$_x$ Epitaxial Thin Films

Superconducting thin films of Fe$_{1.08}$Te:O$_x$ have been epitaxially grown on SrTiO$_3$ substrates by pulsed-laser deposition in controlled oxygen atmosphere. Although the bulk Fe$_{1.08}$Te is not superconducting, thin films with oxygen are superconducting with an onset and a zero resistance transition temperature around 12\,K and 8\,K respectively. Oxygen was found to be crucial to the superconducting properties of these films, suggesting the oxygen can induce superconductivity possibly through substitution of Te. A metal-insulator transition is found at about 60\,K, lower than that of bulk ($\sim$\,70\,K). From magnetoresistive measurements, we obtained the irreversibility line and the upper critical field.