Linear correlation between the c-axis lattice constant and superconducting critical temperature in FeSe0.5Te0.5 thin films

Abstract

Using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electrical resistance analyses, we investigate structural and superconducting properties of FeSe0.5Te0.5 films deposited by pulsed laser deposition on TiO2-buffered (CeO2-buffered) SrTiO3 substrates with the buffer film thickness varying from 0 to several tens of nanometers. It is found that the SrTiO3/TiO2 (or CeO2)/FeSe0.5Te0.5 film in a proper thickness range of the buffer film shows a higher superconducting transition temperature (Tc) than the SrTiO3/FeSe0.5Te0.5 film without buffer layer, indicating that the buffer layer can enhance Tc. Both Tc and the c-axis lattice constant of FeSe0.5Te0.5 films increase first and then decrease with the buffer film thickness, each exhibiting its maximum at a particular buffer film thickness, and both of them show an almost linear correlation.