Saki Inoue, Susumu Yoshizawa, Yu Nakajima, Keiichi Kojima, Takashi Tsukamoto, Takashi Kikukawa and Yuki Sudo. Spectroscopic characteristics of Rubricoccus marinus xenorhodopsin  (RmXeR) and a putative model for its inward H⁺ transport mechanism. Physical Chemistry Chemical Physics, 20, 3172-3183. (2018)