Growth of ultra-thin high-Tc FeSe_0.5Te_0.5 film with high Tc on piezoelectric Pb(Mg_1/3Nb_2/3)_0.7Ti_0.3O₃ substrates by pulsed laser deposition

The influence of strain on the electrical transport properties of iron chalcogenide superconductors FeSexTe1-x may offer insight into the mechanism of superconductivity. The inverse piezoelectric effect from a piezoelectric substrate provides a method of continuous tuning of the lattice deformation on one and the same sample. Single-crystalline piezoelectric Pb(Mg1/3Nb2/3)Ti0.3O3 (PMN-PT) substrates have been shown to allow reversible and dynamic control of biaxial strain in epitaxially grown thin functional films. Here we present an effective method to significantly improve the epitaxy of superconducting FeSe1-xTex thin films via the introduction of a semiconducting buffer layer of FeSe1-xTex. The buffer layer enables subsequent growth of superconducting FeSe1-xTex at reduced deposition temperatures (275°C) on PMN-PT by pulsed laser deposition. The films exhibit consistently high critical temperatures (≥16 K); the FeSe1-xTex thin films show Tc as high as 15 K even when the thicknesses are less than 10 nm. This work demonstrate a versatile platform to investigate the relationship between structure and superconductivity in FeSexTe1-x thin films.