Fluctuation conductivity from charge density waves in pseudo-one-dimensional systems
Bray, James William
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https://hdl.handle.net/2142/30727
Description
Title
Fluctuation conductivity from charge density waves in pseudo-one-dimensional systems
Author(s)
Bray, James William
Issue Date
1974
Doctoral Committee Chair(s)
Bardeen, John
Department of Study
Physics
Discipline
Physics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
fluctuation conductivity
charge density waves
pseudo-one-dimensional systems
Fröhlich conductivity model
Language
en
Abstract
This thesis examines theoretically the Fröhlich conductivity model,
which describes a charge-density-wave phenomenon which can lead to enhanced electrical conductivity in pseudo-one-dimensional systems. The experimental facts concerning pseudo-one-dimensional systems which may illustrate aspects of the Fröhlich mechanism are reviewed. The physical basis of the Fröhlich model is discussed in detail and is extended by the new suggestion that the important Fröhlich mode frequencies are less than
the Kohn anomaly frequency. A phenomenological formulation of the free energy is used to calculate the fluctuation electrical conductivity (paraconductivity) at temperatures where the fluctuations are still mobile.
The result gives values which are somewhat small to account for the largest experimental results. The fluctuation thermal conductivity is calculated
similarly, and its ratio to the paraconductivity is found to be suppressed, very much as in the BCS model. A microscopic model is introduced through the formulation of the Fröhlich collective mode propagator, approximations to which are examined for deficiencies. An approximation to the propagator
is used to calculate diagrammatically the paraconductivity. An attempt is made to resolve disagreement in the literature regarding this calculation, and the correspondence of the mic,oscopic and phenomenological results is discussed. The use of mean-field theory in one dimension limits the validity of these calculations to several degrees above the transition
temperature.
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