Two-level systems and excited-state transitions in fluorite mixed crystals and silica glass
Low-temperature far-infrared absorption measurements have been made on a number of alkaline earth:lanthanum fluoride mixed crystals with the fluorite structure. In the mm wave region a continuous distribution of two-level glassy states is identified as being very similar to that previously found for glasses. At shorter wavelengths a characteristic temperature dependence associated with excited state transitions is observed in these mixed crystals. When silica glass is examined with the same precision, similar excited state transitions are found.
FitzGerald, S.A., J.A. Campbell, and A.J. Sievers. 1994. "Two-level systems and excited-state transitions in fluorite mixed crystals and silica glass." Physical Review Letters 73(23): 3105-3108.
American Physical Society
Physical Review Letters
Physics and Astronomy