Linear correlation between the c-axis lattice constant and superconducting critical temperature in FeSe_0.5Te_0.5 thin films

Abstract

Using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, and electrical resistance analyses, we investigate structural and superconducting properties of FeSe 0.5 Te 0.5 films deposited by pulsed laser deposition on TiO 2 -buffered (CeO 2 -buffered) SrTiO 3 substrates with the buffer film thickness varying from 0 to several tens of nanometers. It is found that the SrTiO 3 /TiO 2 (or CeO 2 )/FeSe 0.5 Te 0.5 film in a proper thickness range of the buffer film shows a higher superconducting transition temperature (T c ) than the SrTiO 3 /FeSe 0.5 Te 0.5 film without buffer layer, indicating that the buffer layer can enhance T c . Both T c and the c-axis lattice constant of FeSe 0.5 Te 0.5 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.

Effects of Te- and Fe-doping on the superconducting properties in FeySe1−xTex thin films

“…1 , only Fe y Se 1− x Te x and TiO 2 peaks are observed along the c -axis (00 l ), which indicates the Fe y Se 1− x Te x films to be the single tetragonal phase. Our previous work confirmed that TiO 2 as a buffer layer could increase the lattice match between Fe(Se, Te) film and STO substrate, so as to enhance the superconducting property of Fe(Se, Te) film 24 . We find that with increasing Te doping, the (00 l ) peaks significantly shift to a low angle.…”

Effects of Te- and Fe-doping on the superconducting properties in FeySe1-xTex thin films

“…1, only FeySe1-xTex and TiO2 peaks are observed along the c-axis (00l), which indicates the FeySe1-xTex epitaxial films to be single tetragonal phase. Our previous work confirmed that TiO2 as a buffer layer could increase the lattice match between Fe(Se, Te) film and STO substrate, so as to enhance the superconducting property of Fe(Se, Te) film [23].…”

Effect of substrate on superconducting and magnetic properties for the epitaxial FeSe0.5Te0.5 thin films

“…As a result, the in-plane and out-of-plane lattice constant are closely related, and the c-axis lattice constant of the FST film changes depending on the lattice mismatch of the interface between FST and TiO 2 -buffered substrate. Since the in-plane lattice constant of TiO 2 is between those of FST and the substrates, the interface between FST and TiO 2 -buffered substrate has smaller lattice mismatch and smaller strain, which is conductive to the superconductivity of the FST [18]. The crystal quality and atom distribution between the interface of FST/TiO 2 heterostructure will be further analyzed by STEM images.…”