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Phase transitions and spin excitations of spin-1 bosons in optical lattice
We investigate ground state properties of spin-1 bosonic system trapped in
optical lattice with extended standard basis operator (SBO) method. For both
ferromagnetic () systems, we
analytically figure out the symmetry properties in Mott-insulator and
superfluid phases, which would provide a deeper insight into the MI-SF phase
transition process. Then by applying self-consistent approach to the method, we
include the effect of quantum and thermal fluctuations and derive the MI-SF
transition phase diagram, which is in quantitative agreement with recent
Monte-Carlo simulation at zero temperature, and at finite temperature, we find
the underestimation of finite-temperature-effect in the mean-field
approximation method. If we further consider the spin excitations in the
insulating states of spin-1 system in external field, distinct spin phases are
expected. Therefore, in the Mott lobes with and atoms per site, we
give analytical and numerical boundaries of the singlet, nematic, partially
magnetic and ferromagnetic phases in the magnetic phase diagrams.Comment: 14 pages, 6 figure
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