Superconducting and structural properties of FeSe$_{x}$Te$_{1-x}$ epitaxial thin films

We report magnetoresistive, critical current density, and structural measurements of superconducting FeSe$_{1-x}$Te$_{x}$ epitaxial thin films grown by pulsed laser deposition. Enhanced onset superconducting transition temperature ($\sim $ 17 K) is observed in FeSe$_{0.5}$Te$_{0.5}$ epitaxial thin films. Structural analysis by x-ray diffraction and high resolution transmission electron microscopy reveal that these films generally have significantly shorter out-of-plane lattice constant $c $than the bulk value, suggesting that the out-of-plane changes have a dominating impact on the superconducting transition in iron-based superconductors. Our data also indicate that the upper critical field $H_{c2}$(0) of those films may reach over 50 T. Flux pinning properties of these films are examined with the help of detailed structural analysis.