The correlated motion of electrons in the presence of strong orbitalfluctuations and correlations is investigated with respect to magneticcouplings and excitations in an orbitally degenerate ferromagnet. Introductionof the orbital degree of freedom results in a class of diagrams representingspin-orbital coupling which become particularly important near the orbitalordering instability. Low-energy staggered orbital fluctuation modes,particularly with momentum near (\pi/2,\pi/2,0) (corresponding to CE-typeorbital correlations), are shown to generically yield strong intrinsicallynon-Heisenberg (1-\cos q)^2 magnon self energy correction, resulting in no spinstiffness reduction, but strongly suppressed zone-boundary magnon energies inthe Gamma-X direction. The zone-boundary magnon softening is found to bestrongly enhanced with increasing hole doping and for narrow-band materials,which provides insight into the origin of zone-boundary anomalies observed inferromagnetic manganites.
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机译：关于轨道退化铁磁体中的磁耦合和激发，研究了存在强烈轨道波动和相关性时电子的相关运动。引入轨道自由度会产生一类表示自旋-轨道耦合的图，这些图在轨道有序不稳定性附近变得尤为重要。低能量交错轨道波动模式，特别是动量接近（\ pi / 2，\ pi / 2,0）（对应于CE型轨道相关性），通常会产生强本征非海森堡（1- \ cos q） ^ 2磁振子自能校正，不会导致自旋刚度降低，但会强烈抑制Gamma-X方向上的区域边界磁振子能量。研究发现，随着空穴掺杂的增加和窄带材料的发展，带边界的磁振子软化作用得到了明显增强，这为深入了解亚铁磁锰矿带边界的异常现象提供了依据。
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