The introduction of “twist” or relative rotation between two atomically thin van der Waals membranes gives rise to periodic moiré potential, leading to a substantial alteration of the band structure of the planar assembly. While most of the recent experiments primarily focus on the electronic-band hybridization by probing in-plane transport properties, here we report out-of-plane thermoelectric measurements across the van der Waals gap in twisted bilayer graphene, which exhibits an interplay of twist-dependent interlayer electronic and phononic hybridization. We show that at large twist angles, the thermopower is entirely driven by a novel phonon-drag effect at subnanometer scale, while the electronic component of the thermopower is recovered only when the misorientation between the layers is reduced to $<6°$. Our experiment shows that cross-plane thermoelectricity at low angles is exceptionally sensitive to the nature of band dispersion and may provide fundamental insights into the coherence of electronic states in twisted bilayer graphene.

中文翻译：

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扭曲双层石墨烯中取向失控的跨平面热电

在两个原子薄的范德华膜之间引入“扭转”或相对旋转会产生周期性的莫尔电位，从而导致平面组件的能带结构发生重大变化。虽然最近的大多数实验主要通过探测面内传输特性来专注于电子带杂交，但在这里我们报告了扭曲的双层石墨烯中范德华间隙上的面外热电测量结果，显示出依赖的层间电子和声子杂交。我们表明，在大扭转角处，热功率完全由亚纳米尺度的新型声子拖曳效应驱动，而仅当层之间的取向错误减小到$<6°$。我们的实验表明，低角度的跨平面热电对能带色散特性极为敏感，并且可以为扭曲的双层石墨烯中电子态的相干性提供基本的见识。