1205.5191 (Alexey Filinov et al.)

Collective and single-particle excitations in 2D dipolar Bose gases    [PDF]

Alexey Filinov, Michael Bonitz

The Berezinskii-Kosterlitz-Thouless transition in 2D dipolar systems has been studied recently by path integral Monte Carlo (PIMC) simulations [A. Filinov et al., PRL 105, 070401 (2010)]. Here, we complement this analysis and study temperature-coupling strength dependence of the density (particle-hole) and single-particle (SP) excitation spectra both in superfluid and normal phases. The dynamic structure factor, S(q,\omega), of the longitudinal excitations is rigorously reconstructed with full information on damping. The SP spectral function, A(q,\omega), is worked out from the one-particle Matsubara Green's function. A stochastic optimization method is applied for reconstruction from imaginary times. Sharp energy resonances of the density response and SP excitations are observed in the superfluid regime even at large wavevectors. The involved hybridization of both spectra is discussed. In contrast, in the normal phase, when there is no coupling to the SP excitations, the density modes, beyond acoustic phonons, are significantly damped. Our results generalize previous zero temperature analyses based on variational many-body wavefunctions [F. Mazzanti et al., PRL 102, 110405 (2009), D. Hufnagl et al., PRL 107, 065303 (2011)], where the underlying physics of the excitation spectrum and the role of the condensate has not been addressed.

View original: http://arxiv.org/abs/1205.5191