Comparison of S- and Te-substitution effects in FeSe thin films*

We have successfully grown single crystalline films of FeSe_1−xS_x with x ≤ 0.43 via pulsed laser deposition. As x increases, the structural transition temperature decreases and the superconducting transition temperature, T_c, shows a gradual decrease even when the structural transition disappears. We observed a new kink structure in the resistivity-temperature curves for films with large x, which is likely due to a magnetic transition. The obtained phase diagram of FeSe_1−xS_x is in contrast to that of FeSe_1−yTe_y films, which shows a sudden increase of Tc at the composition where the structural transition disappears[1]. These results demonstrate that the relationship between the nematicity and the superconductivity is not universal in FeSe, suggesting that the nematicity does not play a primary role in the superconductivity in this system[2].
[1] Y. Imai et al., Sci. Rep. 7, 46653 (2017).
[2] F. Nabeshima et al., J. Phys. Soc. Jpn. 87, 073704 (2018).