Stuttgart 2012 – scientific programme

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A: Fachverband Atomphysik

A 33: SYRA 3: Ultracold Rydberg Atoms and Molecules 3

A 33.7: Talk

Thursday, March 15, 2012, 12:00–12:15, V7.03

Collective and quasiparticle excitations in 2D dipolar gases — •Alexey Filinov und Michael Bonitz — Institut für Theoretische Physik und Astrophysik, Christian-Albrechts-Universität, Leibnizstr. 15, D-24098 Kiel, Germany

The Berezinskii-Kosterlitz-Thouless transition in dipolar atomic, molecular and indirect exciton systems has been recently studied by path integral Monte Carlo simulations [1,2]. Here, we complement these analyses by the spectral densities of the longitudinal collective and single particle (SP) excitations by computing the dynamic structure factor, S(q,ω), and the SP spectral function, A(q,ω), across the superfluid to normal fluid transition. The SP spectrum has been worked out by evaluation of the one-particle Matsubara Green’s function together with a stochastic optimization method for the reconstruction of A(q,ω) from imaginary times. We discuss the coupling of both spectra in the superfluid phase. We observe sharp resonances due to the quasi-condensate. The excitations in the normal phase are shifted to higher energies and significantly damped beyond the acoustic branch. Our results generalize previous zero-temperature analyses based on variational many-body wavefunctions [2,3]. The underlying physics of excitations and the role of the condensate is not easily extracted from such calculations. Moreover, at finite temperatures the use of the variational approach becomes problematic as the excitation damping becomes significant.

[1] A. Filinov et al., PRL 105, 070401(2010); [2] J. Böning et al., PRB 84, 075130(2011); [3] F. Mazzanti et al., PRL 102, 110405(2009); [4] D. Hufnagl et al., PRL 107, 065303(2011)