Self-trapped droplets of ultra-cold gases
M. Özgür Oktel
Abstract: Recently, dipolar gases and two component mixtures were observed to form high density droplets in a regime where mean field theory predicts collapse. The selftrapping of Bosonic atoms is surprising as there is no Pauli exclusion principle to stop them from collapse. These droplets present a novel form of equilibrium where quantum fluctuations are critical for stability. So far, the effect of quantum fluctuations have only been considered at zero temperature through the local chemical potential arising from the Lee--Huang--Yang correction. We extend the theory of dipolar droplets to non-zero temperatures using Hartree--Fock--Bogoliubov theory, and show that the local compressibility is strongly affected by temperature fluctuations. Hartree-Fock--Bogoliubov theory, together with local density approximation for excitations, reproduces the zero temperature results. We find that both the transition between the droplet and trapped states, and the collective oscillation frequencies of the droplet can change dramatically even at typical experimental temperatures (T ~ 100 nK).