A Theoretical Study of Super Fluidity in Spin-orbit Coupled Bose-Einstein Condensate

Abstract

Using the theoretical formalism of Q Zhu et al. [EPL, 109, 50003 92012) and Y. J. Lin et al.[Nature 471, 83 (2011)], we have theoretically studied spin-orbit coupling and super fluidity in SOC coupled Bose Einstein condensate. In this study, we observed the following facts: Spin-orbit coupling plays an essential role in the super fluidity of SOC coupled Bose Einstein condensate. Our theoretical analysis of the Bogoliubov excitation shows that it has two branches (a) one is gapless and phonon like at long wavelength (b) typically gapped. The excitation implies super fluidity which contains distinct new features: (i) Galilean invariance is absent (ii) One cannot define critical velocity of super fluidity independent of the reference frame. The super fluidity depends upon two factors (a) the speed of BEC exceeds a critical value (b) cross-helicity. The cross helicity is defined as the cross product of the spin and kinetic momentum of the BEC.