Self-Trapped States of an Electron in a Structurally Disordered System

Electrons injected into structurally disordered materials may occupy free-electron-like states in a conduction band, band-tail states, some of which will be nondiffusing and are thus localized in the Anderson sense, and, finally, self-trapped states. Eggarter has recently described the first two types of states with specific application to He gas. In the present work, the self-trapped states are discussed. Specific calculations are carried out for He, ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, and Ne in the ideal-gas approximation. Virial corrections are demonstrated for He gas at 4.2 K. Available experimental results, for the four materials mentioned, are discussed in the context of the theory presented and it is shown that for certain regimes of density and temperature self-trapped states exist and play an important role in determining the observed transport parameters. Further calculations and experiments are suggested to probe in detail the characteristics of all the states available to electrons in the type of disordered materials discussed.