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Journal of the Physical Society of Japan

Ground State of Bosons in Bose–Fermi Mixture with Spin–Orbit Coupling

Ryohei Sakamoto, Yosuke Ono, Rei Hatsuda, Kenta Shiina, Emiko Arahata, 弘之 森

Published Jun 16, 2017• 2 citations
Publisher

Abstract

We study an effect of spin-1/2 fermions on the ground state of a Bose system with equal Rashba and Dresselhaus spin–orbit coupling. By using mean-field and tight-binding approximations, we show the ground state phase diagram of the Bose system in the spin–orbit coupled Bose–Fermi mixture and find that the characteristic phase domain, where a spin current of fermions may be induced, can exist even in the presence of a significantly large number of fermions.

DOI
10.7566/jpsj.86.075003

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We study a mixture of Bose and Fermi gases with equal Rashba and Dresselhaus spin–orbit coupling. The phase diagram of bosons with the same coupling was already studied in a mean-field approximation and shown to have three kinds of ground states. In the present study, the ground state of the spin–orbit coupled Bose–Fermi mixture is investigated in the same approach to analyze effects of introducing fermions to the bosonic system. The result shows that even a small amount of fermions could drastically change the phase diagram of the bosons.
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The novel controllability of a spin current in cold atoms is studied. We show that a mixture of spin-1/2 fermions and spin–orbit (SO) coupled pseudospin-1/2 bosons at zero temperature can form a fermionic spin current, which is experimentally controllable with an external laser applied to the bosons to create the SO coupling. We derive the ground-state phase diagram of the bosons using a variational wave function and identify the magnetic structure of each phase. The spin current of the fermions with the background of the spiral/precessed magnetization of the bosons is calculated as a function of the wave vector and intensity of the external laser. We show that the spin current increases and then decreases, forming a peak, as the wave vector of the laser increases, which indicates the controllability of the spin current with the laser parameters.
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We consider a spin-orbit coupled configuration of spin-1/2 interacting bosons with equal Rashba and Dresselhaus couplings. The phase diagram of the system at T=0 is discussed with special emphasis on the role of the interaction treated in the mean-field approximation. For a critical value of the density and of the Raman coupling we predict the occurrence of a characteristic tricritical point separating the spin mixed, the phase separated, and the zero momentum states of the Bose gas. The corresponding quantum phases are investigated analyzing the momentum distribution, the longitudinal and transverse spin polarization, and the emergence of density fringes. The effect of harmonic trapping as well as the role of the breaking of spin symmetry in the interaction Hamiltonian are also discussed.