石墨烯中声子介导的拓扑Floquet能隙闭合：非唯象分析
Phonon-mediated closing of topological Floquet gaps in graphene: Non-phenomenological analysis
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中文总结 AI 辅助
通过非唯象电子-声子耦合分析，发现声子展宽和闭合石墨烯Floquet能隙，解释拓扑态缺失并提出预泵浦声子或改用Dirac系统等缓解策略。
中文摘要 AI 辅助
Floquet能带工程因其通过激光驱动控制材料性质的潜力而受到广泛研究。特别是，Floquet拓扑态已在Bi$_2$Se$_3$表面被测量到。然而，最初预测的石墨烯中的Floquet拓扑能带仍未观察到，相关工作仅测量到非拓扑的Floquet-Bloch态或间接特征。在此，我们理论探索了受圆偏振激光照射且具有非唯象电子-声子（e-ph）耦合的石墨烯。我们表明，由于石墨烯大的零点运动，e-ph相互作用显著展宽了Floquet能带，这与唯象处理预期一致。然而，我们进一步发现，较大的位移$\Gamma$光学声子将Floquet能隙减小约一半，即使在无仪器展宽的情况下也是如此，并且还能诱导如平带等额外特征。这些声子“进入能隙”并使光电子发射特征模糊。包含非$\Gamma$声子会闭合能隙并大大降低可见性。当这些模式与合理预期的仪器展宽耦合时，效应显著加剧。我们的结果对缺失的Floquet拓扑能隙提出了一个解答，并给出了明确的缓解策略：（i）预泵浦相干声子以抵消模糊效应，或（ii）过渡到具有更有利声子统计的Dirac系统。此外，我们的分析提出Floquet拓扑物理在局域区域是活跃的，因此诸如输运等感兴趣的性质应该是可获取的。我们期望这项工作能影响实验分析，并促成最终可能直接观察石墨烯Floquet拓扑的实验装置。
英文摘要
Floquet band engineering has been intensively studied for its potential to control material properties via laser driving. In particular, Floquet topological states have been measured on the surface of Bi$_2$Se$_3$. Nonetheless, the original prediction of Floquet topological bands in graphene remains unobserved, with works only measuring non-topological Floquet-Bloch states or indirect features. Here, we theoretically explore graphene irradiated by circular lasers with non-phenomenological electron-phonon (e-ph) coupling. We show that e-ph interactions substantially broaden Floquet bands due to graphene's large zero-point motion, as expected from phenomenological treatments. However, we further find that larger displacement $Γ$ optical phonons reduce Floquet gaps by about half, even in absence of instrumentation broadening, and can also induce additional features like flat bands. These phonons "enter the gap" and blur photoemission signatures. Including non-$Γ$ phonons closes the gap and greatly reduces visibility. When these modes couple to reasonably expected instrumentation broadening, the effect is significantly exacerbated. Our results propose an answer to the missing Floquet topological gaps and also lead to clear mitigation strategies: (i) Pre-pumping coherent phonons to counteract blurring, or (ii), transition to a Dirac system with more favorable phonon statistics. Moreover, our analysis proposes that Floquet topological physics is alive in localized regions, such that properties of interest like transport should be accessible. We expect this work to impact experimental analysis and lead to set-ups where graphene Floquet topology might finally be directly observed.
发表机构
- Technion Israel Institute of Technology（以色列理工学院）
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