Control of structural transition in FeSe(1−x)Te(x) thin films by changing substrate materials

Iron chalcogenide superconductors FeSe(1−x)Te(x) are important materials for investigating the relation be-tween the superconductivity and the orbital and/or electronic nematic order, because the end member material FeSe exhibits a structural transition without a magnetic phase transition. However, the phase separation occurs in the region of 0.1 ≤ x ≤ 0.4 for bulk samples, and it prevents the complete understanding of this system. Here, we report the successful fabrication of epitaxial thin films of FeSe(1−x)Te(x) with 0 ≤ x ≤ 0.7, which includes the phase-separation region, on LaAlO(3) substrates via pulsed laser deposition. In the temperature dependences of differential resistivity for these films with 0 ≤ x ≤ 0.3, the dip- or peak- anomalies, which are well-known to be originated from the structural transition in FeSebulk samples, are observed at the characteristic temperatures, T*. The doping-temperature (x–T) phase diagram of FeSe(1−x)Te(x) films clearly shows that T* decreases with increasing x, and that T(c) suddenly changes at a certain Te content where T* disappears, which turns out to be commonly observed for both films on LaAlO(3) and CaF(2). These indicate the importance of controlling the structural transition to achieve high T(c) in iron chalcogenides.