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arXiv 1408.7018cond-mat.str-el
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耗尽Kondo-和Anderson-格点模型的强耦合极限

Strong-coupling limit of depleted Kondo- and Anderson-lattice models

Irakli Titvinidze, Andrej Schwabe, Michael Potthoff

摘要:

利用四阶强耦合简并微扰理论导出了具有局域自旋的耗尽系统的Kondo晶格模型的有效低能哈密顿量。在强J极限,完全本地近藤单线态形成的自旋网站绑定一小部分的传导电子。低能理论描述了多余的传导电子在近藤单态的散射以及它们由单态的虚激发产生的有效相互作用。除了Nozieres已经讨论过的Hubbard项之外,我们还发现了铁磁海森堡相互作用、反铁磁同位旋相互作用、相关跳跃,以及在不止一维的情况下的三位和四位相互作用。相互作用项可以被转换成高度对称和形式上简单的自旋形式,使用对称地围绕近藤单线态的成键轨道的自旋。这种旋转是非局部的。我们发现,依赖于耗尽晶格的几何形状,不同的近藤单线态周围的非局域自旋的空间重叠可能会导致铁磁秩序。这是一个严格的论点,适用于半满模型,通过变分分析的稳定性的完全极化的费米海的多余的传导电子,以及精确的对角化的有效模型。在强杂化极限下,对耗尽Anderson晶格进行了类似的四阶微扰分析。即使在不适用Schriling-Wolff变换的参数区域中,这也产生相同的有效理论,尽管具有不同的耦合常数。

英文摘要:

Fourth-order strong-coupling degenerate perturbation theory is used to derive an effective low-energy Hamiltonian for the Kondo-lattice model with a depleted system of localized spins. In the strong-J limit, completely local Kondo singlets are formed at the spinful sites which bind a fraction of conduction electrons. The low-energy theory describes the scattering of the excess conduction electrons at the Kondo singlets as well as their effective interactions generated by virtual excitations of the singlets. Besides the Hubbard term, already discussed by Nozieres, we find a ferromagnetic Heisenberg interaction, an antiferromagnetic isospin interaction, a correlated hopping and, in more than one dimensions, three- and four-site interactions. The interaction term can be cast into highly symmetric and formally simple spin-only form using the spin of the bonding orbital symmetrically centered around the Kondo singlet. This spin is non-local. We show that, depending on the geometry of the depleted lattice, spatial overlap of the non-local spins around different Kondo singlets may cause ferromagnetic order. This is sustained by a rigorous argument, applicable to the half-filled model, by a variational analysis of the stability of the fully polarized Fermi sea of excess conduction electrons as well as by exact diagonalization of the effective model. A similar fourth-order perturbative analysis is performed for the depleted Anderson lattice in the limit of strong hybridization. Even in a parameter regime where the Schrieffer-Wolff transformation does not apply, this yields the same effective theory albeit with a different coupling constant.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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