New Aspects of Photoinduced Paramagnetic States in Chalcogenide Glasses

Abstract

Professor Fritzsche and coworkers have made many important contributions to the study of localized states in amorphous solids. In particular, the seminal work of Cohen, Fritzsche, and Ovshinsky (CF0)¹ set the stage for a decade of intense experimental and theoretical investigations of localization and the nature of localized states. Much of the early work was concerned with the apparently contradictory information obtained with different experimental probes. Specifically, for the case of chalcogenide glasses, the results of transport and other measurements (as reviewed comprehensively by Professor Fritzsche²) were interpreted as evidence for the existence of localized states in the gap of these amorphous solids. The pinning of the Fermi level near mid-gap was cited as incontravertible evidence for a high density of localized states, and estimates of the density of states at the Fermi energy were on the order of 10¹⁸cm^–3.However, early electron spin resonance (ESR) experiments³, specifically the definitive experiments carried out in Professor Fritzsche^’s laboratory, demonstrated that under equilibrium conditions the density of unpaired spins in high purity chalcogenide glasses was less than 10¹⁴cm^–3 The ESR experiments were consistent with the failure to observe Curie paramagnetism at low temperature^4,5, which provided further evidence for the diamagnetism of high purity chalcogenide glasses.