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arXiv 2502.13005cond-mat.str-el
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一维SSH模型中的双极化子动力学

Bipolaron dynamics in the one-dimensional SSH model

Filip Marijanović, Yi-Fan Qu, Eugene Demler

AI总结:

本文采用变分方法研究一维SSH模型中的双极化子,探索全参数范围(含绝热区),揭示其基态、色散及激发谱特性,发现不同相互作用区质量变化规律与宇称选择定则,为理解动量依赖型电子-声子系统多体态提供关键依据。

摘要:

表征双极化子的束缚特性并理解其如何依赖于电子-声子相互作用,对于揭示强相互作用电子-声子系统中涌现的多体态本质至关重要。迄今为止,大多数双极化子研究局限于Holstein模型,其中耦合常数与动量无关。动量依赖型电子-声子相互作用的典型例子来自声子畸变改变电子跳跃的系统,即SSH模型。SSH模型中的单个极化子已比Holstein模型中的对应物更丰富,且随着电子-声子相互作用增强,会出现向有限动量基态的相变。本文采用变分方法研究一维SSH模型中的双极化子,讨论其基态、色散和激发谱。我们探索了系统的全参数范围,包括此前理论研究无法触及的慢声子绝热区。与早期研究一致,我们发现反绝热强相互作用区的双极化子有效质量较低;相比之下,绝热情况下,电子-声子相互作用增强会导致双极化子质量呈指数增长。我们证实了SSH双极化子存在多个束缚激发态分支,并讨论了这些束缚态在动力学中的特征。我们还表明,反绝热区的响应函数遵循宇称选择定则,该定则对激发谱施加对称性约束,为SSH双极化子提供了明确特征。

英文摘要:

Characterizing bipolaron binding, and understanding how it depends on electron-phonon interaction, is crucial to unraveling the nature of emergent many-body states in strongly interacting electron-phonon systems. So far, most studies of bipolarons have been limited to the Holstein model, in which the coupling constant is momentum-independent. The paradigmatic example of momentum-dependent electron-phonon interaction comes from the system in which phonon distortions modify electron hopping, the SSH model. Already individual polarons in the SSH model are richer than the Holstein model counterparts, and feature a phase transition into the finite momentum ground state with increasing electron-phonon interaction. In this paper, we use a variational approach to study bipolarons in the one-dimensional SSH model and discuss their ground state, dispersion, and excitation spectra. We explore the full parameter range of the system, including the adiabatic regime of slow phonons, which was inaccessible to previous theoretical studies. In agreement with earlier studies, we find that in the anti-adiabatic strongly interacting regime, bipolarons have low effective mass. By contrast, in the adiabatic case, we find that increasing electron-phonon interactions results in an exponential increase of the bipolaron mass. We establish the existence of multiple branches of bound excited states of SSH bipolaron and discuss the signatures of these bound states in dynamics. We show that in the anti-adiabatic regime, response functions obey a parity selection rule, that imposes symmetry constraints on the excitation spectra and provides a clear signature of SSH bipolarons.

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