| Rotating two-component Bose-Einstein condensates (BECs) could have a rich variety of vortex phases in addition to the conventional triangular vortex lattice. These different vortex lattice arrangements lead to various spin textures. The realization of spin-orbit (SO) coupling in BECs opens up a new avenue in cold atom physics. In this paper, we investigate the ground-state vortex strctures and spin textures of two-component BECs with rotating or spin-orbit coupling. These structures greatly enrich the ground state phases of Bose-Einstein condensate.Firstly, we study the ground-state properties of rotating two-component Bose-Einstein condensates (BECs) with strong intercomponent repulsion located in a harmonic potential. Due to the strong intercomponent repulsion interaction, the two components depart from each other, forming a pair of shell-like rotating droplets located symmetrically in the trap with a small spatial overlap. Projecting the system into a pseudospin space, two rotating droplets form two spin domains and a spin domain wall is formed at the interface of the two components. When the rotating angular frequency is present, the symmetry of the spin on the x-y plane is broken, and a complex and spatial periodic spin texture is formed on the domain-wall region. We discuss the dependence of the spin texture of the domain wall on the angular velocity in detail. The relation among the number of the vortices, the topological charge and the angular momentum, as an extension of Feynman’s rule in the two-component BECs, is given, based on the spin texture carrying the angular momentum of the condensates.Secondly, we investigate the ground-state properties of rotating two-component BECs confined in an annular potential. For the two-component mixed BECs, we classify the ground states with the Thomas-Fermi approximation (TFA). The analytical approximate results agree well with the numerical calculation results. For the two-component phase-separated BECs with particle number grave imbalance, we also classify their ground states using the TFA, and discuss their spin textures with numerical calculation. What’s exciting is that we find a spin texture which cannot be achieved in harmonic potential:Concentric Double-Annulus Skyrmion. The emergence of the topological excitations greatly enrichs the ground state phases of the two-component BECs.Finally, we investigate the transitions of ground states induced by zero momentum (ZM) coupling in pseudospin-1/2 Rashba spin-orbit (SO) coupled BECs. In a weak harmonic trap, the ZM coupling induces an imnbalanced momentum distribution, and leads to the decrease of the amplitude of stripe state. When the strength of ZM coupling exceeds a critical value, the ground state of the condensate experiences the transition from stripe phase to PW phase. Besides, the ZM coupling can also achieve the transition from ZM phase to PW phase. In a strong harmonic trap, the ground state of the condensate usually presents vortex-lattice phase, and the wave function can be regarded as a superposition of n plane waves of single particle ground state, where n=3,4,6. These different momentum distributions of the vortex lattice phases will lead to different vortex lattice arrangements. We take n=3 as an example to study the effect of ZM coupling on the vortex lattice phase. For the positive effective Rabi frequency of ZM coupling, the condensate is driven from a vortex lattice phase to a vortex-free lattice phase and finally to a PW phase with the increase of coupling strength. And for the negative effective Rabi frequency, the condensate is driven from a vortex lattice phase to a stripe phase, and finally to a PW phase. |
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