Condensation of quasiparticles and density modulation beyond the superfluid critical velocity

Sütő, András and Szépfalusy, Péter (2013) Condensation of quasiparticles and density modulation beyond the superfluid critical velocity. PHYSICAL REVIEW A, 88 (4). ISSN 2469-9926

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Abstract

We extend our earlier study of the ground state of a bosonic quasiparticle Hamiltonian by inves- tigating the effect of a constant external velocity field. Below a critical velocity the ground state is a quasiparticle vacuum, corresponding to a pure superfluid phase at zero temperature. Beyond the critical velocity energy minimization leads to a macroscopic condensation of quasiparticles at a nonzero wave vector kv parallel to the velocity v. Simultaneously, physical particles also undergo a condensation at kv and, to a smaller extent, at −kv. Together with the Bose-Einstein condensation at k = 0, the three coexisting condensates give rise to density modulations of wave vectors kv and 2kv. For larger |v| our model predicts a bifurcation of kv with corresponding two pure condensates and no density modulation.

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