The surrounding hydrogen gas pressure at room temperature was varied to convert rare earth hydride films from metallic mirrors to insulating windows. The critical exponents of the metal insulator transitions were determined using conductivity and Hall measurements. The important role played by the electron-electron interactions was justified by the large values of the product of the static and dynamical critical exponents.
Hoekstra, A. F. T., Roy, A. S., Rosenbaum, T. F., Griessen, R. P., Wijngaarden, R. J., & Koeman, N. J. (2001). Light-induced metal-insulator transition in a switchable mirror. Physical Review Letters, 86, 5349-5352. https://doi.org/10.1103/PhysRevLett.86.5349