High Frequency Dielectric Response in Dipolar Systems
Some thirty seven years ago Onsager rescued us from the embarrassment of a theoretical analysis of dielectrics which, however justifiably renowned otherwise, implied that all dipolar liquids should exhibit a spontaneous polarization below temperatures typically hundreds of degrees K. The crucial role his analysis and introduction of cavity and reaction fields has played in all subsequent theory of the static and low frequency response of dipolar systems hardly requires comment or review here. What we should like to show in our contribution on this occasion is that a comparatively simple generalization to the dynamical case of the model he employed in 1936 gives rise to a quite compact dielectric function ɛ(k,ω) which provides a perhaps surprisingly complete description of the response of dipolar liquids at all frequencies below those associated with molecular distortion. Since derivations of the form of ʵ (k, ω) rely on one or another form of fluctuation-dissipation theorem and hence ultimately on microscopic reversibility there is at least a double connection to Onsager’s work. In keeping with the title of this conference, we note that in the work on which we report can he found contacts, beyond the obvious ones, with quantum field theory, the fully interacting electron liquid, and superfluids; and properties of polar liquids are surely important in biophysicsphysics.
KeywordsDielectric Function Dielectric Response Collective Mode Reaction Field Orientational Response
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