Thursday, March 28, 2013

1303.6903 (Yun Li et al.)

Superstripes and the excitation spectrum of a spin-orbit-coupled
Bose-Einstein condensate

Yun Li, Giovanni I. Martone, Lev P. Pitaevskii, Sandro Stringari
Using Bogoliubov theory we calculate the excitation spectrum of a spinor Bose-Einstein condensed gas with equal Rashba and Dresselhaus spin-orbit coupling in the stripe phase. The emergence of a double gapless band is pointed out as a key signature of Bose-Einstein condensation and of the spontaneous breaking of translational invariance symmetry. In the long wavelength limit the lower and upper branches exhibit, respectively, a clear spin and density nature. For wave vectors close to the first Brillouin zone the lower branch acquires an important density character responsible for the divergent behavior of the structure factor and of the static response function. The sound velocities are calculated as functions of the Raman coupling for excitations propagating orthogonal and parallel to the stripes. Our predictions provide new perspectives for the identification of supersolid phenomena in ultracold atomic gases.
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