1. S. I Pekar:Untersuchungen über die Elektronentheorie der Kristalle (Akademie-Verlag, Berlin, 1954), a translation ofS. I. Pekar:Issledovania po electronnoi teorii kristallov (Gostekhizdat, Moscow-Leningrad, 1951). Physical nature, solid-state applications, and the early methods of investigation of the polaron model. A summary of the previous work in the field is given.
2. H. Fröhlich, H. Pelzer andS. Zinau:Properties of slow electrons in polar materials, Philos. Mag.,41, 221 (1950). Quantum mechanics of the electron brought into the dielectric continuum of an ionic crystal: the lowest energy levels, polaron size, velocity, mean free path, the question of self-trapping.
3. N. N. Bogolubov:On a new form of the adiabatic perturbation theory in the problem of interaction of a particle with a quantum field, Ukr. Math. J.,2, 3 (1950). An original form of the strong-coupling perturbation theory is developed, based on the exact separation of the translational degree of freedom. Canonical transformations and variational considerations of different types are extensively used.
4. S. V. Tyablikov:To a theory of interaction of a particle with a quantum field, Ž. Ėksp. Teor. Fiz. [Sov. Phys. JETP],21, 16 (1951). The polaron model in a weak-coupling regime is treated via canonical-transformation method: the ground-state energy, effective mass, low-lying excitations and an account of temperature effects.
5. T. D. Lee, F. E. Low andD. Pines:The motion of slow electrons in a polar crystal, Phys. Rev.,90, 297 (1953). A quantum-mechanical treatment via canonical transformations and variational principles: the low-lying energy levels, effective mass, effective radius, the mean number of phonons in a cloud around the electron; weak-and intermediate-coupling regimes.