ANTARES Beamline, Synchrotron SOLEIL and Université Paris-Saclay , L'Orme des Merisiers, Saint Aubin-BP 48, 91192 Gif sur Yvette Cedex, France.
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences , Beijing 100190, China.
Nano Lett. 2018 Feb 14;18(2):1082-1087. doi: 10.1021/acs.nanolett.7b04604. Epub 2018 Jan 9.
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.
范德华异质结构是由层状材料垂直堆叠而成，为新奇的量子现象提供了新的机会，而这些现象在其组成成分中是不存在的。在这里，我们报告了在石墨烯/六方氮化硼（h-BN）异质结界面处极化子准粒子的出现。使用纳米点角分辨光发射谱，我们观察到 h-BN 价带最大值的角隅复制，其能量间隔与异质结构的最高声子能量一致，这表明由于向前散射电子-声子耦合而形成了 Fröhlich 极化子。对 h-BN 能带进行抛物线拟合得到有效质量增强约 2.3，表明耦合强度为中等。我们基于 Migdal-Eliashberg 理论的理论模拟与实验结果相符，允许提取微观物理参数。此外，由于与 h-BN 带的杂化，观察到石墨烯 π 带的重整化。我们的工作将极化子研究从过渡金属氧化物推广到具有更高材料灵活性的范德华异质结构，突出了层间耦合作为探索新兴现象的额外自由度。
