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arXiv 1406.6472cond-mat.str-elcond-mat.mes-hall
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二维有限蜂窝晶格中四电子问题的精确基态

Exact ground state for the four-electron problem in a 2D finite honeycomb lattice

Reka Trencsenyi, Konstantin Glukhov, Zsolt Gulacsi

摘要:

在一个维数远小于全希尔伯特空间维数的子空间中,我们推导出了含有六角重复单元的二维样品中的精确四粒子基态,并用Hubbard模型描述.该过程首先确定一个小的子空间${\cal{S}}$中的基态$|Ψ_g\rangle$放置,然后推导出$|Ψ_g\rangle$在${\cal{S}}$的精确对角化。小的子空间是通过反复应用哈密顿量$\hat H$在一个精心选择的描述最相互作用的粒子配置的起始波矢量上,以及由应用$\hat H$产生的波矢量上,直到所获得的方程组本身闭合为止而获得的。原则上可应用于固定但任意系统尺寸和粒子数的程序本身是有趣的,因为它为使用类似策略的数值近似技术提供了精确信息,但为${\cal{S}}$应用非完整基础。${\cal{S}}$内部的对角化提供了关于激发光谱的低位部分的不完整图像,但提供了精确的$|Ψ_g\rangle$。一旦得到了精确的基态,就可以很容易地分析它的性质。发现$|Ψ_g\rangle$总是作为单重态,有趣的是,其能量在$U \to \infty$极限饱和。非近似计算结果表明,不同粒子组态在基态的出现几率呈现出二维正方形Hubbard系统所不具有的“颤动”特征.因此,局部库仑排斥在二维正方形和蜂窝型系统中的表现形式存在差异,这可能是多体行为差异的真正来源。

英文摘要:

Working in a subspace with dimensionality much smaller than the dimension of the full Hilbert space, we deduce exact 4-particle ground states in 2D samples containing hexagonal repeat units and described by Hubbard type of models. The procedure identifies first a small subspace ${\cal{S}}$ in which the ground state $|Ψ_g\rangle$ is placed, than deduces $|Ψ_g\rangle$ by exact diagonalization in ${\cal{S}}$. The small subspace is obtained by the repeated application of the Hamiltonian $\hat H$ on a carefully chosen starting wave vector describing the most interacting particle configuration, and the wave vectors resulting from the application of $\hat H$, till the obtained system of equations closes in itself. The procedure which can be applied in principle at fixed but arbitrary system size and number of particles, is interesting by its own since provides exact information for the numerical approximation techniques which use a similar strategy, but apply non-complete basis for ${\cal{S}}$. The diagonalization inside ${\cal{S}}$ provides an incomplete image about the low lying part of the excitation spectrum, but provides the exact $|Ψ_g\rangle$. Once the exact ground state is obtained, its properties can be easily analyzed. The $|Ψ_g\rangle$ is found always as a singlet state whose energy, interestingly, saturates in the $U \to \infty$ limit. The unapproximated results show that the emergence probabilities of different particle configurations in the ground state present "Zittern" (trembling) characteristics which are absent in 2D square Hubbard systems. Consequently, the manifestation of the local Coulomb repulsion in 2D square and honeycomb types of systems presents differences, which can be a real source in the differences in the many-body behavior.

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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