Self-trapped states of electrons in dense fluids

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Abstract
The conditions which lead to electron self-trapping, in a material, are theoretically investigated. The theory is developed for the simple case of a dense fluid, composed of a single kind of atom, obeying the ideal gas equation of state, and interacting with an electron as a system of hard-sphere scatterers. Possible generalizations are noted. A static continuum approximation and statistical considerations define configurations in which atoms feel no net force, electron states are obtained for these configurations, and, then, stability is investigated. The theory developed is shown to reduce to the case first investigated by Toyozawa, in the limit of small distortions (from the average configuration in the absence of the electron). The material-electron coupling constant depends on the average density, and since the stiffness of the materials is shown to be the external pressure, both may be continuously and independently varied experimentally. The results, for arbitrary distortions, lead to stable self-trapping and metastable quasifree electrons for strong coupling, weak stiffness; stable quasifree electrons and unstable self-trapping for weak coupling, strong stiffness; and metastable self-trapping in a limited intermediate regime. The different regimes are delimited quantitatively. The theoretical importance of this work resides in the fact that the generally used adiabatic approximation can only be justified for system states near stable or metastable configurations. The experimental consequences of changes in the stability of configurations are dramatic changes in some properties. For example, the observed electron-drift-mobility plunge in fluid helium is shown to be strongly correlated with the predicted transition of self-trapped states to stability.