Terahertz Quantum Electronics of Carbon Nanostructures: Population Inversion, Gain and Coherent Bandgap Engineering

将当今逻辑和调制设备的开关速度限制和集成密度推进到太赫兹(每秒一万亿个周期)和20纳米以下的挑战是整个信息处理、记录和通信领域的基础。这一挑战可以通过一种新的太赫兹量子纳米电子学范式来应对，这种新型范例基于超快相干激光泵浦石墨烯--一个原子厚的蜂窝状碳材料--和单壁碳纳米管--由卷起的石墨烯单分子层组成。研究人员将使用可见光以外的短脉冲太赫兹光和超快相机技术来直接监测这些碳纳米材料中光激发态的形成和时间演变。这一新方法将使他们能够在飞秒尺度上捕捉和控制其新颖的电磁特性，或精确到一万亿分之一秒。这些成果将带来展示其巨大发展潜力的诱人机会，例如，超过千兆赫的光调制器、从红外到太赫兹的宽带增益介质、辐射控制的热电子晶体管、响应从太赫兹到可见光频率的超宽带电磁辐射的多功能设备。我们在这场“超快”和“超小型”挑战中的成功，将揭示开发新一代光电子器件的尚未发现的物理过程，并为支持信息革命和21世纪的数字经济提供前景。在这项提案中，教育是不可或缺的重要组成部分。它包括相互关联的具体教育计划，横跨小型大学教授/本科生的教育计划，面向高中教师和他们的学生的“物理日”计划，面向未被充分代表的少数族裔学生的宣传，并为他们提供研究/培训机会。相干光激发如何控制单壁碳纳米管中的激子玻色子和石墨烯单分子膜中的狄拉克费米子是量子和光电子技术中最基本但又交叉的问题之一。该提案旨在探索这些碳纳米结构中一些引人注目的激光驱动的量子过程，并展示它们在设备应用方面的巨大潜力。主要目标是：确定强光激发石墨烯单分子膜的宽带增益谱和阈值；利用强太赫兹脉冲在狄拉克锥体附近展示相干的光驱动带隙开放；研究石墨烯中极端的中红外和远红外非线性混频；利用双光子激发的暗激子态在单壁碳纳米管中实现太赫兹受激发射。及时推进的途径在于结合超短太赫兹脉冲，专门制造的高质量的单层和几层石墨烯和碳纳米管，以及从太赫兹到可见光谱区域的超宽带探测能力。这项提议已经确定了令人信服的机会，以在当今一些最令人兴奋的材料中推进碳纳米结构的动态、非平衡和非线性方面的最糟糕的领域之一。瞄准问题存在于几个前沿领域，如物质的量子光学控制、太赫兹电子传输和超快光电子技术。尽管已经在进行复杂的理论研究，但所提出的探索广泛预测的基本现象的实验计划已经落后。这些原始的结果是变革性的，为基于石墨烯和碳纳米管的太赫兹以上速度调制器、可饱和吸收材料和超宽带增益介质打开了可能性。

The challenge of pushing the switching speed-limit and integration density of today's logic and modulation devices into the terahertz (one trillion cycles per second) and sub-20 nanometer regime underlies the entire field of information processing, recording and communication. This challenge may be met by a novel paradigm of terahertz quantum nano-electronics based on ultrafast coherent laser pumping in graphene - one atom thick, the honeycomb-shaped carbon material - and single-walled carbon nanotubesthe rolled-up sheets of graphene monolayers. Researchers will use short pulsed terahertz light, outside the visible spectrum, and an ultrafast camera technique to directly monitor the formation and time evolution of photo-excited states in these carbon nanomaterials. This novel method will allow them to capture and control their novel electromagnetic properties on the femtosecond scale, or to one quadrillionth of a second. The results will open fascinating opportunities to demonstrate their significant potential to advance, e.g., above-gigahertz light modulators, broadband gain mediums from the infrared to terahertz, radiation controlled hot-electron transistors, multi-functional devices responding to ultrabroadband electromagnetic radiations from the terahertz to visible frequency. Our success in this "ultrafast" and "ultrasmall" challenge will reveal as-yet-undiscovered physical processes for developing new generation optoelectronic device and offer perspectives for sustaining the information revolution and the 21st century's digital economy. Education is an integral and essential component in this proposal. It consists of interconnected, specific plans for education that span small college professors/undergraduates, "A Physics Day" program for high school teachers and their students; outreach to underrepresented minority students and provision of research/training opportunities to them.How coherent photoexcitations control excitonic bosons in single-walled carbon nanotubes and Dirac fermions in graphene monolayers is among the most fundamental, yet cross-cutting, issues in quantum and optoelectronic technologies. The proposal aims to explore some remarkable laser-driven quantum processes in these carbon nanostructures and demonstrate their significant potential for device applications. The primary goals are: to determine broadband gain spectrum and threshold in strongly photoexcited graphene monolayers; to demonstrate coherently photo-driven, bandgap opening near the Dirac cone using intense terahertz pulses; to investigate extreme mid-infrared and far-infrared nonlinear wave mixing in graphene; to achieve terahertz stimulated emission in single-walled carbon nanotubes using two-photon excited, dark exciton states. The approach for the timely advancement lies in the combination of ultrashort terahertz pulses, specially fabricated, high quality mono- and few-layer graphene and carbon nanotubes, and ultra-broadband probe capability from the terahertz to visible spectral regions. This proposal has identified compelling opportunities to advance one of the most poorly- addressed territories in some most exciting materials today dynamical, non-equilibrium, and nonlinear aspects of carbon nanostructures. The targeting problems are in the boundaries of several frontiers such as quantum optical control of matter, terahertz electrical transport, and ultrafast optoelectronic technology. Although sophisticated theoretical studies have been underway, the experimental schemes for exploring a wide range of the predicted fundamental phenomena, as proposed, have lagged behind. These original results are transformative, opening the possibility for graphene- and carbon nanotube- based above-terahertz speed modulators, saturable absorbers, ultra-broadband gain medium.