Dynamic scaling at MIT in yttrium hydride switchable mirrors

Yttrium hydride demonstrates a remarkable transition of its electronic and optical properties upon change of hydrogen concentration: a thin YHx film can be continuously and reversibly brought from a shiny metal at x = 2 to a transparent dielectric at x = 3, by changing pressure of the surrounding hydrogen gas [1]. It has been showed that the metal-insulator transition (MIT) could be neatly passed under constant hydrogen pressure by changing the carrier doping via ultraviolet illumination at low temperatures [2]. Pronounced electron-electron interactions are posited to lead to the opening of a large optical gap. The established scaling laws of the conductivity with temperature and doping [2] are strong indications for the quantum nature of the metalinsulator transition in YHx. To shed more light on the quantum nature of the MIT, the frequency dependence of conductivity is very informative. In an extensive frequency range, frequency ! and temperature T will influence the conductivity in a similar way, which will lead to a so-called !/T -scaling behaviour. In this talk results on the optical conductivity in the sub-terahertz regime will be presented.