Isotope effects in switchable metal-hydride mirrors

Measurements of optical reflectance, transmittance, and electrical resistiv ity on the switchable mirror systems YHx and YDx show that the absorption o f hydrogen induces the same variations as that of deuterium. in both cases there is a weak transparency window for the metallic dihydride (dideuteride ) phase and a yellowish transparency in the insulating trihydride (trideute ride) phase. The slightly higher electrical resistivity of the deuterides i s related to the lower energy of their optical phonons. The absence of sign ificant isotope effects in the optical properties of YHx (YDx) is at varian ce with Peierls-like theoretical models, It is, however, compatible with st rong electron correlation models.