Many-Body Ultrafast Light-Matter Interactions in Two-Dimensional Graphene Optoelectronics

非技术描述：最近发现的石墨烯，一种单原子厚度的材料，刺激了凝聚态物理的显著进步，以及纳米级器件应用，涵盖电子，热学和机械领域。在芯片级光电子学和光学物理学中，石墨烯具有独特的光吸收，仅由光和电子之间的相互作用决定。该项目研究并推进石墨烯中多体光物质相互作用的光电子学，特别是超快光学，光电探测器中的多电子电流产生，以及下一代光开关和调制器。研究涉及激光-材料相互作用、非线性光学、材料表征和同步材料-器件物理。与此同时，利用先进的基础科学，教育活动包括拓展到东洛杉矶少数民族高中和教师，与工程和多样性卓越中心合作，为低收入的未被充分代表的第一代大学生提供服务，以及开设一门新的固态光电子研究生/本科课程。技术描述：石墨烯独特的线性和无质量带结构，在纯二维狄拉克费米子结构中，使光学片的导电性具有显著的频率无关性，具有从可见光到中红外波长的宽带光学特性。由于sp2杂化二维态的低密度，潜在的带间光学跃迁可以通过Dirac点附近的电门控进行显著调谐，具有可调谐的基于电荷密度的费米能级。在这个项目中，首席研究员研究了石墨烯光电子学中的多体光物质相互作用，包括电子-电子、电子-声子、电子-光子散射机制和动力学。这些相互作用的目标是器件物理和应用在超快光学（第一推力）、多载流子光电流动力学（第二推力）和电光学（第三推力）。第一部分研究了石墨烯中的全光学非线性，如四波混频和非线性动力学：这包括连续波和脉冲测量，石墨烯中的门可调谐费米能级和载流子动力学。第二部分研究了石墨烯-硅结构中光电光电流的产生：这涉及光电流映射和与单片硅结构的比较，门偏载流子动力学，以及电子输运中的热载流子倍增。第三个重点是通过带间和带内转换研究高速电光调制器：这涉及到在拉曼表征和表面声子工程的支持下，从超过100 GHz的载波频率到甚至太赫兹的水平。费米能级调谐，非线性信号检测技术，以及表面材料控制和处理，实现了独特的器件物理。在亚皮秒时间尺度上的多体散射动力学为石墨烯基下一代光电子学的基础材料和原子层工程研究提供了肥沃的土壤。

Non-technical description: The recent discovery of graphene, a material of single atomic thickness, has spurred remarkable advances in condensed matter physics as well as, nanometer-scale device applications covering electronic, thermal and mechanical domains. In chip-scale optoelectronics and optical physics, graphene has a unique optical absorption defined solely by the interaction between light and electrons. This project examines and advances the many-body light-matter interactions in graphene towards optoelectronics, particularly for ultrafast optics, for multi-electron current generation in photodetectors, and for next-generation optical switches and modulators. The research involves laser-material interactions, nonlinear optics, material characterization, and synchronized material-device physics. In parallel and leveraging the fundamental science advanced, the education activity involves outreach to East Los Angeles minority-heavy high-schools and teachers, partnership with the Center for Excellence in Engineering and Diversity for low-income underrepresented first-generation college-bound youth, and a new graduate/undergraduate course on solid-state optoelectronics. Technical description: The unique linear and massless band structure of graphene, in a purely two-dimensional Dirac fermionic structure, has enabled an optical sheet conductivity that is remarkably frequency-independent, with broadband optical character spanning from visible to mid-infrared wavelengths. The underlying interband optical transitions can be tuned significantly via electric gating near the Dirac point, with a tunable charge-density-based Fermi level due to the low density of sp2-hybridized two-dimensional states. In this project the principal investigator examines the many-body light-matter interactions in graphene optoelectronics covering the electron-electron, electron-phonon, electron-photon scattering mechanisms and dynamics. These interactions are targeted towards device physics and applications in ultrafast optics (first thrust), multi-carrier photocurrent dynamics (second thrust), and electro-optics (third thrust). The first thrust examines all-optical nonlinearities such as four-wave mixing and nonlinear dynamics in graphene: this involves continuous-wave and pulsed measurements, with the gate-tunable Fermi levels in graphene and carrier dynamics. The second thrust examines optoelectronic photocurrent generation in graphene-silicon structures: this involves photocurrent mapping and comparison with monolithic silicon structures, gated-bias carrier dynamics, and hot carrier multiplication in electronic transport. The third thrust examines high-speed electro-optic modulators through interband and intraband transitions: this involves working with carrier frequencies in excess of 100 GHz to even the THz level, supported by Raman characterization and surface phonon engineering. Fermi level tuning, nonlinear signal detection techniques, along with surface material control and processing, are implemented to enable the unique device physics. The many-body scattering dynamics - each at the sub-picosecond timecales - provide a fertile ground for fundamental material and atomic layer engineering studies in graphene-based next-generation optoelectronics.