2014/09/30 by Juraj Radic, Juraj Radić, Stefan S. Natu +1
Physics and Astronomy · #Cold Atom Physics and Bose-Einstein Condensates #Condensed matter physics #Ferromagnetism #Hamiltonian (control theory) #Phase (matter) #Phase diagram #Phase transition #Physics #Physics of Superconductivity and Magnetism #Quantum mechanics #Quantum, superfluid, helium dynamics #Superfluidity #cond-mat.quant-gas #quant-ph
paper · pdf · doi:10.1103/physrevlett.113.185302
published as Phys. Rev. Lett. 113 185302 (2014) · 5 pages, 3 figures. published version
openalex publication_date 2014/10/31 · arxiv created 2014/11/11 · arxiv updated 2014/11/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We compute the finite-temperature phase diagram of a pseudospin-1/2 Bose gas with contact interactions, using two complementary methods: the random-phase approximation and self-consistent Hartree-Fock theory. We show that the spin-dependent interactions, which break the (pseudo-) spin-rotational symmetry of the Hamiltonian, generally lead to the appearance of a magnetically ordered phase at temperatures above the superfluid transition. In three dimensions, we predict a normal easy-axis (easy-plane) ferromagnet for sufficiently strong repulsive (attractive) interspecies interactions, respectively. The normal easy-axis ferromagnet is the bosonic analog of Stoner ferromagnetism known in electronic systems. For the case of interspecies attraction, we also discuss the possibility of a bosonic analog of the Cooper-paired phase. This state is shown to significantly lose in energy to the transverse ferromagnet in three dimensions, but is more energetically competitive in lower dimensions. Extending our calculations to a spin-orbit-coupled Bose gas with equal Rashba and Dresselhaus-type couplings (as recently realized in experiment), we investigate the possibility of stripe ordering in the normal phase. Within our approximations, however, we do not find an instability towards stripe formation, suggesting that the stripe order melts below the condensation temperature, which is consistent with the experimental observations of Ji et al. [Ji et al., Nat. Phys. 10, 314 (2014)].