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This paper studies the superfluidity of ultracold spin-2 Bose atoms with weak interactions in optical lattices by calculating the excitation energy spectrum using the Bogoliubov approach. The energy spectra exhibit the characteristics of the superfluid-phase explicitly and it finds the nonvanishing critical speeds of superfluid. The obtained results display that the critical speeds of superfluid are different for five spin components and can be controlled by adjusting the lattice parameters in experiments. Finally it discusses the feasibilities of implementing and measuring superfluid.

In this paper we develop a variational theory to study the dynamic properties of ultracold Bose gas in a funnel external potential. We obtain one-dimensional nonlinear equation which describes the dynamics of transverse tight confined bosonic gas from three-dimension to one-dimension, and find one-dimensional s-wave scattering length which depends on the shape of transverse confining potential. If the funnel trapping potential is strong enough at zero temperature, all transverse excitations are frozen. We find the dynamic equation which describes the Tonks–Girardeau gas and present a qualitative analysis of the experimental accessibility of the Tonks–Girardeau gas with funnel-trapped alkalic atoms.

This paper presents a funnel external potential model to investigate dynamic properties of ultracold Bose gas. By using variational method, we obtain the ground-state energy and density properties of ultracold Bose atoms. The results show that the ultracold Bose gas confined in a funnel potential experiences the transition from three-dimensional regime to quasi-one-dimensional regime in a small aspect ratio, and undergoes fermionization process as the aspect ratio increases.

Based on the collinear and non-collinear magnetic structures, the ground state, magnetism and electronic structure of the frustrated triangular antiferromagnet AgCrO2 have been investigated using the density functional theory (DFT) within the generalized gradient approximation (GGA) with the projected augmented wave (PAW) method. Detailed magnetic structure has been elucidated vividly from the theoretical view. The calculations show that AgCrO2 magnetic ground state has 120° helical-spin order with its spiral plane parallel to the (110)or (11-0) plane. Due to the strong intra- and interlayer geometric spin frustration, parallel helical-spin chains arise along the a,b or a+b direction with the screw-rotation angle 120°. From the non-collinear electronic structure calculation, it is found that due to the spin frustration Cr-3d orbital states near the Fermi level become more localized, indicating an enhanced interaction between Cr-Cr. Nevertheless, the spin-orbit coupling has weak influence on the electron structure.