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arXiv 2307.07613cond-mat.str-el
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二维Su-Schrieffer-Heeger模型的相和奇异相变

Phases and Exotic Phase Transitions of a Two-Dimensional Su-Schrieffer-Heeger Model

Anika Götz, Martin Hohenadler, Fakher F. Assaad

AI总结:

本研究通过辅助场量子蒙特卡洛模拟探究二维Su-Schrieffer-Heeger模型的相图,揭示了不同参数区域的多种相态及相变特征,为理解相关电子-声子系统提供了新结果。

摘要:

我们通过辅助场量子蒙特卡洛模拟研究了正方晶格上的Su-Schrieffer-Heeger电子-声子模型。加入一种对称性允许的相互作用后,可对声子进行解析积分,代价是引入具有虚时关联的离散Hubbard-Stratonovich场。我们采用单自旋翻转和全局更新方法,研究了O(4)对称点处作为跃迁$t$和声子频率$ω_0$函数的相图。当$t=0$时,电子跃迁由玻色子辅助,该模型可映射为无约束$\n \mathbb{Z}_2$规范理论。一个关键物理量是每个 plaquette 上涌现的有效通量,在辅助跃迁区域其值等于$π$,在大$t$时则为零。前一区域的相可通过涌现狄拉克费米子的不稳定性来理解。我们的结果支持随着$ω_0$升高,$(π,0)$价键固体(VBS)相与反铁磁(AFM)相之间存在直接连续相变。在大$t$、小$ω_0$的情况下,我们发现了有限温度特征——一种无序赝能隙相,对应此前报道的与嵌套不稳定性相关的$(π,π)$VBS基态。随着$ω_0$升高,会再次出现AFM有序态。

英文摘要:

We study a Su-Schrieffer-Heeger electron-phonon model on a square lattice by means of auxiliary-field quantum Monte Carlo simulations. The addition of a symmetry-allowed interaction permits analytical integration over the phonons at the expense of discrete Hubbard-Stratonovich fields with imaginary-time correlations. Using single-spin-flip and global updates, we investigate the phase diagram at the O(4)-symmetric point as a function of hopping $t$ and phonon frequency $ω_0$. For $t=0$, where electron hopping is boson assisted, the model maps onto an unconstrained $\mathbb{Z}_2$ gauge theory. A key quantity is the emergent effective flux per plaquette, which equals $π$ in the assisted-hopping regime and vanishes for large $t$. Phases in the former regime can be understood in terms of instabilities of emergent Dirac fermions. Our results support a direct and continuous transition between a $(π,0)$ valence bond solid (VBS) and an antiferromagnetic (AFM) phase with increasing $ω_0$. For large $t$ and small $ω_0$, we find finite-temperature signatures, a disordered pseudogap phase, of a previously reported $(π,π)$ VBS ground state related to a nesting instability. With increasing $ω_0$, AFM order again emerges.

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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