Emergence of Interfacial Polarons from Electron–Phonon Coupling in Graphene/h-BN van der Waals Heterostructures,Nano Letters

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Emergence of Interfacial Polarons from Electron–Phonon Coupling in Graphene/h-BN van der Waals Heterostructures
Nano Letters ( IF 9.6 ) Pub Date : 2018-01-09 00:00:00 , DOI: 10.1021/acs.nanolett.7b04604
Chaoyu Chen ₁ , José Avila ₁ , Shuopei Wang ₂ , Yao Wang _{3,

4,

5} , Marcin Mucha-Kruczyński _{6,

7} , Cheng Shen ₂ , Rong Yang ₂ , Benjamin Nosarzewski _{3,

4} , Thomas P. Devereaux _{4,

8} , Guangyu Zhang ₂ , Maria Carmen Asensio ₁

Affiliation

van der Waals heterostructures, vertical stacks of layered materials, offer new opportunities for novel quantum phenomena which are absent in their constituent components. Here we report the emergence of polaron quasiparticles at the interface of graphene/hexagonal boron nitride (h-BN) heterostructures. Using nanospot angle-resolved photoemission spectroscopy, we observe zone-corner replicas of h-BN valence band maxima, with energy spacing coincident with the highest phonon energy of the heterostructure, an indication of Fröhlich polaron formation due to forward-scattering electron–phonon coupling. Parabolic fitting of the h-BN bands yields an effective mass enhancement of ∼2.3, suggesting an intermediate coupling strength. Our theoretical simulations based on Migdal–Eliashberg theory corroborate the experimental results, allowing the extraction of microscopic physical parameters. Moreover, renormalization of graphene π-band is observed due to the hybridization with the h-BN band. Our work generalizes the polaron study from transition metal oxides to van der Waals heterostructures with higher material flexibility, highlighting interlayer coupling as an extra degree of freedom to explore emergent phenomena.

中文翻译：

石墨烯/ h-BN van der Waals异质结构中电子-声子耦合产生的界面极化子

van der Waals异质结构，垂直堆叠的层状材料为组成成分中不存在的新型量子现象提供了新的机遇。在这里，我们报告极化子准粒子在石墨烯/六方氮化硼（h-BN）异质结构的界面处的出现。使用纳米点角度分辨光发射光谱，我们观察到了h-BN价带最大值的区域角复制品，其能量间隔与异质结构的最高声子能量重合，这是由于前向散射电子-声子耦合而形成Fröhlich极化子的迹象。。h-BN带的抛物线拟合产生了约2.3的有效质量增强，表明具有中等耦合强度。我们基于Migdal–Eliashberg理论的理论模拟证实了实验结果，允许提取微观物理参数。此外，由于与h-BN带的杂交，观察到石墨烯π带的重新归一化。我们的工作概括了从过渡金属氧化物到具有更高材料柔韧性的范德华异质结构的极化子研究，强调层间耦合是探索出现现象的额外自由度。

更新日期：2018-01-09

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