Dynamical theory for fluctuations and phase transitions in orbitally degenerate electron systems

考虑轨道涨落的理论框架的制定我们扩展了平均场理论以考虑涨落效应。新理论在无限空间维度的极限下变得精确，并被视为经典自旋的球面模型近似的量子力学扩展。我们的理论比其他用定域费米子表示自旋的理论更进一步。CeB_6和Ce_<0.75>La_<0.25> b_6轨道简并电子系统中奇怪磁序的解释我们通过假设次近邻位之间的伪偶极相互作用来解释CeB_6第三相奇怪磁序的起源。此外，我们还讨论了在Ce_<0.75>La_<0.25>B_6中新发现的IV相存在八极序的可能性。我们发现了一个新的相位，它在能量上接近于已经观察到的相，并且可以在单轴压力等外场的存在下实现。我们发展了新的泛函的i…More的积分形式来在微观上执行金兹堡-朗道展开。轨道简并电子系统中的自旋波和轨道波激发我们从复杂的自旋轨道有序态推导出了基本激发的色散关系。含有16个Ce离子的大细胞产生48个分支。我们推导了所有分支，并找到了光谱与多极相互作用之间的特征关系。特别是一些分支沿波矢量的某些方向几乎是平坦的，这可以用中子衍射来验证。轨道简并一维系统的精确动力学到目前为止，我们解释了三维系统的结果。在低维中，波动的作用要重要得多。为了更清楚地看到这种情况，我们研究了一个一维的完全可溶模型。该模型具有SU(4)对称性来表示简并度，并且相互作用与距离的平方（1/γ^2）成反比。我们成功地准确地推导出了动力相关函数。少

Formulation of theoretical framework with account of orbital fluctuations We extended the mean-field theory to take account of fluctuation effects. The new theory becomes exact in the limit of infinite spatial dimensions, and is regarded as a quantummechanical extension of the spherical model approximation for classical spins. Our theory goes one step beyond the other ones that use localized fermions to represent spins.Explanation of the strange order in orbitally degenerate electron systems such as CeB_6 and Ce_<0.75>La_<0.25>B_6We explained origin of strange magnetic order in the phase III of CeB_6 by assuming a pseudo-dipolar interaction between next-nearest-neighbor sites. Furthermore, we discussed possibility of an octupole order for the newly found phase IV in Ce_<0.75>La_<0.25>B_6. We found a new plase which lies energetically close to the already observed phases, and which may be realized in the presence of external field such as uniaxial pressure. We developed new functional i … More ntegral formalism to perform the Ginzburg-Landau expansion microscopically.Spin and orbital wave excitations in orbitally degenerate electron systemsWe derived the dispersion relations of elementary excitations from the complicated spinorbital ordered state. The large unit cell with 16 Ce ions give rise to 48 branches. We derived all branches and found characteristic relation between the spectrum and the multipolar interaction. In particular some branches are almost flat along certain directions of wave vector, which may be checked by neutron diffraction.Exact dynamics of orbitally degenerate one-dimensional systemsSo far we explained results for three-dimensional systems. In low dimensions, the role of fluctuations is much more important. In order to see the situation most clearly, we studied an exactly soluble model in one dimension. This model has the SU (4) symmetry to represent the degeneracy, and the interaction is inversely proportional to the square of the distance (1/γ^2). We succeeded in deriving the dynamical correlation function exactly. Less