Superfluid Breakdown and Multiple Roton Gaps in Spin-Orbit Coupled Bose-Einstein Condensates on an Optical Lattice

Abstract

We investigate the superfluid phases of a Rashba spin-orbit coupled Bose-Einstein condensate residing on a two dimensional square optical lattice in the presence of an effective Zeeman field $\Omega$. At a critical value $\Omega ={\Omega }_c$, the single-particle spectrum $E_k$ changes from having a set of four degenerate minima to a single minimum at $k=0$, corresponding to condensation at finite or zero momentum, respectively. We describe this quantum phase transition and the symmetry breaking of the condensate phases. We use the Bogoliubov theory to treat the superfluid phases and determine the phase diagram, the excitation spectrum and the sound velocity of the phonon excitations. A novel dynamically unstable superfluid regime occurring when $\Omega$ is close to ${\Omega }_c$ is analytically identified and the behavior of the condensate quantum depletion is discussed. Moreover, we show that there are two types of roton excitations occurring in the $\Omega <{\Omega }_c$ regime and obtain explicit values for the corresponding energy gaps.

4 pages, 2 figures, revised version. Accepted for publication in Phys. Rev. A Rapid Communications

References in corpus (5)

• Spin-Orbit Coupled Spinor Bose-Einstein Condensates
• $p_x+i{p}_y$ superfluid from s-wave interactions of fermionic cold atoms
• Bose Hubbard Models with Synthetic Spin-Orbit Coupling: Mott Insulators, Spin Textures and Superfluidity
• Anisotropic dynamics of a spin-orbit coupled Bose-Einstein condensate
• Stability of ultracold atomic Bose condensates with Rashba spin-orbit coupling against quantum and thermal fluctuations

Cited by in corpus (7)

• Degenerate Quantum Gases with Spin-Orbit Coupling
• Measurement of collective excitations in a spin-orbit-coupled Bose-Einstein condensate
• Gap Solitons in Spin-Orbit-Coupled Bose-Einstein Condensates in Optical Lattices
• Phase separation in a spin-orbit coupled Bose-Einstein condensate
• Spontaneous symmetry breaking in a spin-orbit coupled $f=2$ spinor condensate
• Quantum Phase Transition of Bosons in a Shaken Optical Lattice
• Competing interactions in population-imbalanced two-component Bose-Einstein condensates