Growth of Superconducting Epitaxial Films of Sulfur Substituted FeSe via Pulsed Laser Deposition

We report the successful growth of epitaxial thin films of FeSe1−xSx with x ≤ 0.43 via pulsed laser deposition. As S content increases, the nematic transition temperature, Ts, decreases systematically and the superconducting transition temperature, Tc, shows a gradual decrease even when x exceeds the nematic end point (NEP), similar to bulk samples. A new kink anomaly was observed in the ρ–T curves for films with large x, which is likely due to a magnetic transition. The obtained phase diagram of FeSe1−xSx thin films is in contrast to that of FeSe1−yTey films, which shows a rapid increase of Tc at the NEP. Our results demonstrate that the relation between the nematic order and the superconductivity is not universal in the FeSe system, suggesting that the nematic transition does not play a primary role in the superconductivity in these materials.