

Preprint 59/2008
Dispersion forces in a nondegenerate polaron gas
Gennady Chuev
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Submission date: 23. Sep. 2008
Pages: 36
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Abstract:
Using the Feynman path integral method and a theory of polarizable fluids, I evaluate
properties of nondegenerate Fr¨ohlich polarons interacting in the strong coupling
limit. At large enough densities and temperatures these properties are found to be
mainly governed by the dispersion forces, i.e. attractive van-der-Waals interactions,
which are no attributed to any permanent electric multipoles. Neglecting short-range
correlations in the polaron gas, I have obtained an explicit expression for the dispersion
contribution to the free energy of the system. The analysis of this contribution
indicates that the dispersion effect is nonlinear and strongly cooperative at large
enough densities of the polaron gas. The quasiparticles attract due to these forces
leading to softening of the absorption peak, negativity of the dielectric function, and
divergence of compressibility of the system. The main consequence of the dispersion
forces is a quantum transition which results in a dielectric catastrophe considered as
the onset of metallization. A possible excitonic phase consisting from quasiparticles
with a nonzero dipole momentum is also examined. Comparing experimental data
for metal-ammonia solutions, alkali-halide molten salts, and high-Tc superconducting
cuprates, I find that dispersion forces may govern the behavior of self-trapped
carries in these compounds.