Probing the bright exciton state in twisted bilayer graphene via resonant Raman scattering
Probing the bright exciton state in twisted bilayer graphene via resonant Raman scattering
复制标题
DOI：
10.1063/5.0049458
复制
发表时间：
2021-07-05
影响因子：
4
通讯作者：
Yan, Jun
中科院分区：
文献类型：
--
作者：
DeCapua, Matthew C.;Wu, Yueh-Chun;Yan, Jun
双层石墨烯的能带结构是可调的，通过在两层之间引入相对扭转角，解锁奇异相，如超导体和莫特绝缘体，并为新物理学提供肥沃的土壤。在大约10度的中间扭转角处，高度简并的电子跃迁杂交以形成激子态，这在金属系统中是非常不寻常的现象。我们使用共振拉曼散射测量来探测亮激子模式，以跟踪对应于E-2g声子的石墨烯拉曼G峰的强度的演变。通过低温冷却样品，我们能够解决作为激发能量的函数的G峰强度演化中的入射和出射共振，亮激子作为拉曼过程中的中间态的突出表现。对于扭转角为8.6度的样品，我们报告了一个弱的温度依赖的共振展宽γ近似为0.07 eV。在小的非均匀加宽的极限中，在存在由用于拉曼测量的光脉冲激发的电荷和激子的情况下，所观察到的伽马将亮激子散射寿命的下限设置在10 fs处，这受限于石墨烯中的快速激子-激子和激子-电荷散射。
The band structure of bilayer graphene is tunable by introducing a relative twist angle between the two layers, unlocking exotic phases, such as superconductors and Mott insulators, and providing a fertile ground for new physics. At intermediate twist angles around 10 degrees, highly degenerate electronic transitions hybridize to form excitonic states, a quite unusual phenomenon in a metallic system. We probe the bright exciton mode using resonant Raman scattering measurements to track the evolution of the intensity of the graphene Raman G peak, corresponding to the E-2g phonon. By cryogenically cooling the sample, we are able to resolve both the incoming and outgoing resonances in the G peak intensity evolution as a function of excitation energy, a prominent manifestation of the bright exciton serving as the intermediate state in the Raman process. For a sample with twist angle 8.6 degrees, we report a weakly temperature dependent resonance broadening gamma approximate to 0.07 eV. In the limit of small inhomogeneous broadening, the observed gamma places a lower bound for the bright exciton scattering lifetime at 10 fs in the presence of charges and excitons excited by the light pulse for the Raman measurement, limited by the rapid exciton-exciton and exciton-charge scattering in graphene.