The optical properties of the superconducting single crystal Rb0.8Fe1.68Se2 with Tc≃ 31 K have been measured over a wide frequency range in the ab plane. We found that the optical conductivity is dominated by a series of infrared-active phonon modes at low-frequency region as well as several other high-frequency bound excitations. The low-frequency optical conductivity has rather low value and shows quite small Drude-like response, indicating low carriers density in this material. Furthermore, the phonon modes increase continuously in frequency with decreasing temperature; specifically, the phonon mode around 200 cm−1 shows an enhanced asymmetry effect at low temperatures, suggesting an increasing electron-phonon coupling in this system.
@article{arxiv.1405.6781,
title = {Electron-phonon coupling in the superconducting single crystal Rb$_{0.8}$Fe$_{1.68}$Se$_2$},
author = {B. Xu and Y. M. Dai and J. Han and K. Wang and R. Yang and Y. X. Yang and W. Zhang and H. Xiao and X. G. Qiu},
journal= {arXiv preprint arXiv:1405.6781},
year = {2015}
}