Spin excitations and sum rules in the Heisenberg antiferromagnet.
Spin excitations and sum rules in the Heisenberg antiferromagnet.
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海森堡反铁磁体中的自旋激励和求和规则。
DOI：
10.1103/physrevb.49.6710
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发表时间：
1993
期刊：
影响因子：
--
通讯作者：
Stringari
中科院分区：
文献类型：
--
作者：
Stringari
利用和规则的形式，给出并讨论了海森堡反铁磁体中集体激发能的各种界限。我们发现，由于多个磁子对能量加权和规则的不可忽略的贡献，费曼近似大大高估了自旋速度(在S=1/2正方形晶格中高估了约30%)。我们还讨论了一个明显依赖于序参数(交错磁化强度)的不同的Goldstone类型的束缚。这一界限与具有q无关归一化因子的经典自旋波理论的色散成正比。文中还给出了各向异性海森堡模型中激发能的严格界限。
Various bounds for the energy of collective excitations in the Heisenberg antiferromagnet are presented and discussed using the formalism of sum rules. We show that the Feynman approximation significantly overestimates (by about 30% in the S=1/2 square lattice) the spin velocity due to the non-negligible contribution of multiple magnons to the energy-weighted sum rule. We also discuss a different, Goldstone-type bound depending explicitly on the order parameter (staggered magnetization). This bound is shown to be proportional to the dispersion of classical spin-wave theory with a q-independent normalization factor. Rigorous bounds for the excitation energies in the anisotropic Heisenberg model are also presented.