Acoustic dispersion in a two-dimensional dipole system

Abstract

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/r^3 potential at arbitrary degeneracy. Such a system has no RPA limit and the calculation has to include correlations from the outset. We follow the Quasi-Localized Charge (QLC) approach, accompanied by Molecular Dynamics (MD) simulations. Similarly to what has been recently reported for the closely spaced classical electron-hole bilayer [G. J. Kalman et al. Phys. Rev. Lett. 98, 236801 (2007)] 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 [Astrakharchik et al, Phys. Rev. Lett. 98, 060405 (2007)], there is a good agreement between the QLCA kinetic sound speeds and the standard thermodynamic sound speeds in both the classical and quantum domains.

37 pages, submitted to Phys. Rev. B

References in corpus (5)

• Strongly correlated 2D quantum phases with cold polar molecules: controlling the shape of the interaction potential
• Quantum phase transition in a two-dimensional system of dipoles
• Wigner supersolid of excitons in electron-hole bilayers
• Effects of strong correlations for 2D Bose-Einstein condensed dipolar excitons
• Collective excitations in electron-hole bilayers