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arXiv 2105.06802cond-mat.str-el
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Nagaoka铁磁性的自旋自适应全组态相互作用量子蒙特卡罗基准研究

Benchmark study of Nagaoka ferromagnetism by spin-adapted full configuration interaction quantum Monte Carlo

Sujun Yun, Werner Dobrautz, Hongjun Luo, Ali Alavi

摘要:

采用自旋自适应($SU(2)$守恒)全组态相互作用量子蒙特卡罗方法研究了二维单空穴哈伯德模型中的Nagaoka铁磁性。这种方法使我们能够获得有限哈伯德晶格的所有可能自旋态$S$的基态能量,这里针对多达24个位点的晶格获得了各种相互作用强度($U$)。临界相互作用强度,$U_c$,在那里的长冈转变发生的确定为每个晶格,并发现是成比例的晶格尺寸为较大的晶格。低于$U_c$的整体基态被发现有利于最小的总自旋($S=\frac 1 2$),没有中间自旋状态被发现是大于16个站点的晶格上的整体基态。然而,在$U_c$,所有的自旋态的能量被发现是近简并,这意味着可以预期在长冈转变附近的总自旋的大的波动。

英文摘要:

We investigate Nagaoka ferromagnetism in the two-dimensional Hubbard model with one hole using the spin-adapted ($SU(2)$ conserving) full configuration interaction quantum Monte Carlo method. This methodology gives us access to the ground state energies of all possible spin states $S$ of finite Hubbard lattices, here obtained for lattices up to 24 sites, for various interaction strengths ($U$). The critical interaction strength, $U_c$, at which the Nagaoka transition occurs is determined for each lattice and is found to be proportional to the lattice size for the larger lattices. Below $U_c$ the overall ground states are found to favour the minimal total spin ($S=\frac 1 2$), and no intermediate spin state is found to be the overall ground state on lattices larger than 16 sites. However, at $U_c$, the energies of all the spin states are found to be nearly degenerate, implying that large fluctuations in total spin can be expected in the vicinity of the Nagaoka transition.

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