We calculate the full density response function and from it the long-wavelength acoustic dispersion for a two-dimensional system of strongly coupled point dipoles interacting through a 1/ r3 potential at arbitrary degeneracy. Such a system has no random-phase-approximation (RPA) limit and the calculation has to include correlations from the outset. We follow the quasilocalized charge (QLC) approach, accompanied by molecular-dynamics (MD) simulations. Similarly to what has been recently reported for the closely spaced classical electron-hole bilayer and in marked contrast to the RPA, we report a long-wavelength acoustic phase velocity that is wholly maintained by particle correlations and varies linearly with the dipole moment p. The oscillation frequency, calculated both in an extended QLC approximation and in the Singwi-Tosi-Land-Sjolander approximation, is invariant in form over the entire classical to quantum domains all the way down to zero temperature. Based on our classical MD-generated pair distribution function data and on ground-state energy data generated by recent quantum Monte Carlo simulations on a bosonic dipole system, there is a good agreement between the QLC approximation kinetic sound speeds and the standard thermodynamic sound speeds in both the classical and quantum domains.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - Jul 8 2008|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics