Theory of the Contribution of Excitons to the Complex Dielectric Constant of Crystals

J. J. Hopfield
Phys. Rev. 112, 1555 – Published 1 December 1958
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Abstract

It is shown that the ordinary semiclassical theory of the absorption of light by exciton states is not completely satisfactory (in contrast to the case of absorption due to interband transitions). A more complete theory is developed. It is shown that excitons are approximate bosons, and, in interaction with the electromagnetic field, the exciton field plays the role of the classical polarization field. The eigenstates of the system of crystal and radiation field are mixtures of photons and excitons. The ordinary one-quantum optical lifetime of an excitation is infinite. Absorption occurs only when "three-body" processes are introduced. The theory includes "local field" effects, leading to the Lorentz local field correction when it is applicable. A Smakula equation for the oscillator strength in terms of the integrated absorption constant is derived.

  • Received 16 July 1958

DOI:https://doi.org/10.1103/PhysRev.112.1555

©1958 American Physical Society

Authors & Affiliations

J. J. Hopfield*

  • Physics Department, Cornell University, Ithaca, New York

  • *Present address: Bell Telephone Laboratories, Murray Hill, New Jersey.

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Issue

Vol. 112, Iss. 5 — December 1958

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