Effect of Rashba spin-orbit and Rabi couplings on the excitation spectrum of binary Bose-Einstein condensates

Abstract

We present the collective excitation spectrum analysis of binary Bose-Einstein condensates (BECs) with spin-orbit (SO) and Rabi couplings in a quasi-two-dimensional system. In particular, we investigate the role of SO and Rabi coupling strengths in determining the dynamical stability of the coupled BECs using Bogoliubov-de Gennes (BdG) theory. Using the eigenergy of BdG spectrum, we confirm the existence of phonon, roton, and maxon modes with weak repulsive intra-and interspecies contact interactions. The depth of the minimum corresponding to the roton mode depends strongly on the coupling strength. We find that the increase of the SO coupling leads to instability, while the increase in the Rabi coupling stabilizes the system. Also the eigenvectors of BdG spectrum indicates the presence of density like mode in the stable regime and spin like modes in unstable regimes. A phase diagram demonstrating the stability regime in the plane of SO and Rabi coupling strengths is obtained. Finally, we complement the observation of the excitation spectrum with the direct numerical simulation results of coupled Gross-Pitaevskii equations.

Influence of Rashba spin-orbit and Rabi couplings on the miscibility and ground state phases of binary Bose-Einstein condensates

“…We consider a pseudospin-1/2 Bose-Einstein condensates, with Rashba spin-orbit and Rabi couplings trapped under a harmonic potential with strong axial confinement. The properties of such a SO coupled BECs can be described by a set of coupled Gross-Pitaevskii (GP) equations in dimensionless form as [29,33]:…”

“…This state finally transforms into a diagonally unpolarized SW-II. The emergence of unpolarized stripe waves is the conse-quence of the superposition of the eigenstates of non-zero momentum states with different energies [29,65]. The x-component of the spin density vector (S x ) plays an important role in total spin polarization.…”

“…The SO coupling in BECs not only offers a unique testing ground to simulate the response of charged particles to an electromagnetic field but also paves a way to an entirely new paradigm for studying strong correlations of the quantum many-body system, which leads to various symmetry-broken ground state phases such as half-quantum vortex phase and stripe phase [8,9], which researchers claim to show supersolid character [10]. Recent experimental realization of twodimensional (2D) SO coupled BECs [11][12][13] has activated a large amount of theoretical works describing many ground state phases [14][15][16][17][18][19][20][21][22] and elementary excitations [23][24][25][26][27][28][29].…”

“…Apart from this, there are analytical and numerical works that report odd-petal number state and persistent flow [41]. It has been demonstrated that SO coupled BECs may display some bright and dark soliton excitations [23][24][25][26][27][28][29].…”