Real-space observation of vibrational strong coupling between propagating phonon polaritons and organic molecules
Real-space observation of vibrational strong coupling between propagating phonon polaritons and organic molecules
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DOI：
10.1038/s41566-020-00725-3
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发表时间：
2020-11-23
期刊：
影响因子：
35
通讯作者：
Hillenbrand, Rainer
中科院分区：
文献类型：
--
作者：
Bylinkin, Andrei;Schnell, Martin;Hillenbrand, Rainer
货车德瓦耳斯材料中的声子极化激元可以强烈增强中红外频率下的光-物质相互作用，这是由于它们的极端场约束和长寿命（1-7）。声子极化激元因此具有与分子振动强耦合的潜力。虽然用声子-极化激元纳米谐振器在光谱上观察到了振动强耦合的开始（8），但没有实验解决了真实的空间和传播模式中的振动强耦合。在这里，我们证明了纳米成像，振动强耦合之间可以实现薄货车范德华晶体（六方氮化硼）和相邻的薄分子层的分子振动传播声子极化激元。我们进行了近场极化激元干涉测量，表明振动强耦合导致在其色散中具有明显的反交叉区域的传播混合模式的形成，其中发现负群速度的传播。数值计算预测了纳米薄分子层和少层货车德瓦耳斯材料中的声子极化激元的振动强耦合，这可能使传播声子极化激元成为超灵敏芯片光谱和强耦合实验的有前途的平台。实空间中红外纳米成像揭示了非结构化薄六方氮化硼层中分子和传播声子极化激元之间的振动强耦合，为强耦合和化学性质的局部控制提供了实验平台。
Phonon polaritons in van der Waals materials can strongly enhance light-matter interactions at mid-infrared frequencies, owing to their extreme field confinement and long lifetimes(1-7). Phonon polaritons thus bear potential for vibrational strong coupling with molecules. Although the onset of vibrational strong coupling was observed spectroscopically with phonon-polariton nanoresonators(8), no experiments have resolved vibrational strong coupling in real space and with propagating modes. Here we demonstrate by nanoimaging that vibrational strong coupling can be achieved between propagating phonon polaritons in thin van der Waals crystals (hexagonal boron nitride) and molecular vibrations in adjacent thin molecular layers. We performed near-field polariton interferometry, showing that vibrational strong coupling leads to the formation of a propagating hybrid mode with a pronounced anti-crossing region in its dispersion, in which propagation with negative group velocity is found. Numerical calculations predict vibrational strong coupling for nanometre-thin molecular layers and phonon polaritons in few-layer van der Waals materials, which could make propagating phonon polaritons a promising platform for ultrasensitive on-chip spectroscopy and strong-coupling experiments.Real-space mid-infrared nanoimaging reveals vibrational strong coupling between molecules and propagating phonon polaritons in unstructured, thin hexagonal boron nitride layers, which could provide a platform for testing strong coupling and local control of chemical properties.