Optics of Solid State Phase Transformations
The optical spectra of Mott insulators and amorphous semiconductors are discussed in detail, and are contrasted with the spectra of ordinary crystalline semiconductors. Particular emphasis is placed on the transition-metal oxides and the chalcogenide glasses. The major difference between the spectra of such materials and those of the more common semiconductors arise from the breakdown of the k-conservation selection rules and the presence of intrinsic localized states.
The striking changes in the optical properties of materials that exhibit conductivity anomalies are analyzed. In particular, temperature-induced insulator-metal transitions and photo-induced amorphous-crystalline transitions are discussed. The former often yield striking changes in optical properties, transforming from a material transparent in the infrared with an absorption edge to one of high reflectivity with a plasma edge. The latter transformations can shift the absorption edge to lower energy, resulting in a transition from a material transparent to light of a given frequency to one opaque at the same frequency. The reversibility of such transformations and the resolution obtainable using modern laser technology suggest the application of photon-induced amorphous-crystalline transitions as optical memories of extremely high packing density. In addition, write, erase, and read operations can be accomplished with the same laser.
KeywordsAbsorption Edge Crystallization Rate Interband Transition Chalcogenide Glass Mott Transition
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