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

Aftab Alam1, S. C. Prasad2 and L. K. Mishra3

1S/o Gaulam Rasool, Muni Masizad, Gewal Bigha, Gaya-823001, Bihar, INDIA. 2Retd. Associate Professor, Department of Physics, Gaya College Gaya-823001, Bihar, INDIA. 3Department of Physics, Magadh University, Bodh Gaya-824234, Bihar, INDIA.

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.

Keywords : Spin-orbit coupling, Spin-orbit coupled super fluidity, Topological insulators, Spin Hall effect, Spintronic devices, Rashba spin interaction term, Dresselhaus spin interaction term, Bogoliubov excitation, critical velocity, Cross-helicity. INTRODUCTION