Mehew Jake Dudley, Merino Rafael Luque, Ishizuka Hiroaki, Block Alexander, Mérida Jaime Díez, Carlón Andrés Díez, Watanabe Kenji, Taniguchi Takashi, Levitov Leonid S, Efetov Dmitri K, Tielrooij Klaas-Jan
Catalan Institute of Nanoscience and Nanotechnology (ICN2), BIST and CSIC, Campus UAB, 08193 Bellaterra (Barcelona), Spain.
ICFO - Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology (BIST), Castelldefels 08860, Spain.
Sci Adv. 2024 Feb 9;10(6):eadj1361. doi: 10.1126/sciadv.adj1361.
Understanding electron-phonon interactions is fundamentally important and has crucial implications for device applications. However, in twisted bilayer graphene near the magic angle, this understanding is currently lacking. Here, we study electron-phonon coupling using time- and frequency-resolved photovoltage measurements as direct and complementary probes of phonon-mediated hot-electron cooling. We find a remarkable speedup in cooling of twisted bilayer graphene near the magic angle: The cooling time is a few picoseconds from room temperature down to 5 kelvin, whereas in pristine bilayer graphene, cooling to phonons becomes much slower for lower temperatures. Our experimental and theoretical analysis indicates that this ultrafast cooling is a combined effect of superlattice formation with low-energy moiré phonons, spatially compressed electronic Wannier orbitals, and a reduced superlattice Brillouin zone. This enables efficient electron-phonon Umklapp scattering that overcomes electron-phonon momentum mismatch. These results establish twist angle as an effective way to control energy relaxation and electronic heat flow.
理解电子-声子相互作用至关重要，对器件应用具有关键意义。然而，在接近魔角的扭曲双层石墨烯中，目前尚缺乏这种理解。在此，我们使用时间分辨和频率分辨光电压测量作为声子介导的热电子冷却的直接和互补探针，来研究电子-声子耦合。我们发现在接近魔角的扭曲双层石墨烯中冷却速度显著加快：从室温冷却到5开尔文的冷却时间为几皮秒，而在原始双层石墨烯中，对于更低温度，冷却到声子的过程变得慢得多。我们的实验和理论分析表明，这种超快冷却是超晶格形成与低能量莫尔声子、空间压缩的电子万尼尔轨道以及缩小的超晶格布里渊区共同作用的结果。这使得能够进行有效的电子-声子倒逆散射，从而克服电子-声子动量不匹配。这些结果确立了扭曲角作为控制能量弛豫和电子热流的有效方法。
