Low temperature crystal structure and large lattice discontinuity at Tc in superconducting FeTeOx films

Abstract

We report a high resolution x-ray diffraction study of the crystal structure of superconducting FeTeOx films. The crystal symmetry of FeTeOx matches the parent FeTe, unlike most iron-based superconductors. However, at the superconducting transition there is a large change in the c-axis lattice parameter. Such a discontinuity in the thermal expansion is known in normal-to-superconducting phase transitions, but here the effect is far larger than for other iron-based superconductors. Following the typical analysis of such a discontinuity in thermal expansion using the Ehrenfest-relation leads to a prediction of a large enhancement of Tc in strained FeTeOx films.