Exotic superfluidity in spin-orbit coupled Bose-Einstein condensates
1 International Center for Quantum Materials, Peking University - 100871, Beijing, China
2 Department of Physics and Astronomy, Washington State University - Pullman, WA, 99164 USA
Received: 5 July 2012
Accepted: 20 November 2012
We study the superfluidity of a spin-orbit coupled Bose-Einstein condensate (BEC) by computing its Bogoliubov excitations, which are found to have two branches: one is gapless and phonon-like at long wavelength; the other is typically gapped. These excitations imply superfluidity that has two new features: i) due to the absence of the Galilean invariance, one can no longer define the critical velocity of superfluidity independent of the reference frame; ii) the superfluidity depends not only on whether the speed of the BEC exceeds a critical value, but also on cross-helicity that is defined as the direction of the cross-product of the spin and the kinetic momentum of the BEC.
PACS: 03.75.Kk – Dynamic properties of condensates; collective and hydrodynamic excitations, superfluid flow / 03.75.Mn – Multicomponent condensates; spinor condensates / 05.30.Jp – Boson systems
© EPLA, 2012