近日，北京大学的刘开辉及其研究小组与中国科学院物理研究所的孟胜等人合作并取得一项新进展。经过不懈努力，他们揭示扭曲双层石墨烯范霍夫奇点处异常热载流子热化的证据。相关研究成果已于2024年6月18日在国际知名学术期刊《科学通报》上发表。

本文采用时间分辨超快光致发光（PL）自相关光谱技术，深入探讨了TBG（扭曲双层石墨烯）中光激发热载流子的动力学特性。研究人员成功证明了在范霍夫奇点（VHSs）之间，存在一种非传统的超快PL发射现象，其弛豫寿命显著延长了约4倍。

这种独特的光激发载流子行为被归因于超高压下的瓶颈效应，以及层间电荷分布过程导致的异常热载流子热化现象。此项研究对TBG中热载流子动力学的探索，为理解石墨烯双电系统的激发态及其相关物理机制提供了新见解。

据悉，层间扭曲引起了扭曲双层石墨烯(TBG)的光学和电子特性的革命性变化，用于电子学，光子学和光电子学。虽然人们已经对TBG中的基态响应进行了广泛而清晰的研究，但其光激发载流子态的动力学过程仍然难以捉摸。

附：英文原文

Title: Evidence of abnormal hot carrier thermalization at van Hove singularity of twisted bilayer graphene

Author: Sheng Meng c, Kaihui Liu a d, Hao Hong a e

Issue&Volume: 2024/06/18

Abstract: Interlayer twist evokes revolutionary changes to the optical and electronic properties of twisted bilayer graphene (TBG) for electronics, photonics and optoelectronics. Although the ground state responses in TBG have been vastly and clearly studied, the dynamic process of its photoexcited carrier states mainly remains elusive. Here, we unveil the photoexcited hot carrier dynamics in TBG by time-resolved ultrafast photoluminescence (PL) autocorrelation spectroscopy. We demonstrate the unconventional ultrafast PL emission between the van Hove singularities (VHSs) with a ～4 times prolonged relaxation lifetime. This intriguing photoexcited carrier behavior is ascribed to the abnormal hot carrier thermalization brought by bottleneck effects at VHSs and interlayer charge distribution process. Our study on hot carrier dynamics in TBG offers new insights into the excited states and correlated physics of graphene twistronics systems.

DOI: 10.1016/j.scib.2024.06.019

Source: https://www.sciencedirect.com/science/article/abs/pii/S2095927324004444