We systematically studied in-plane optical conductivity of FeSe1−xTex thin films fabricated on CaF2 substrates for x = 0, 0.1, 0.2, and 0.4. This system shows a large enhancement of superconducting transition temperature Tc at x∼ 0.2 and a gentle decrease in Tc with further increasing x. The low-energy optical conductivity spectrum is described by the sum of narrow and broad Drude components, associated with coherent and incoherent charge dynamics, respectively. With increasing Te content, the spectral weight of the narrow Drude component decreases, while the total weight of the two Drude components increases. As a consequence, the fraction of the narrow Drude weight significantly decreases, indicating that Te substitution leads to stronger electronic correlations. Below the nematic transition temperature, the narrow Drude weight decreases with decreasing temperature. This indicates the reduction of the coherent carrier density, resulting from the Fermi-surface modification induced by the development of the orbital order. The reduction of the narrow Drude weight with temperature stopped at x∼ 0.2, corresponding to the disappearance of the nematic transition. Our result suggests that the increase in the coherent carrier density induced by the suppression of the nematic transition gives rise to the enhancement of Tc. The decrease in Tc with further Te substitution likely arises from too strong electronic correlations, which are not favorable for superconductivity.
@article{arxiv.2103.13659,
title = {Evolution of charge dynamics in FeSe$_{1-x}$Te$_{x}$: Effects of electronic correlations and nematicity},
author = {M. Nakajima and K. Yanase and M. Kawai and D. Asami and T. Ishikawa and F. Nabeshima and Y. Imai and A. Maeda and S. Tajima},
journal= {arXiv preprint arXiv:2103.13659},
year = {2021}
}