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

将当今逻辑和调制器件的开关速度限制和集成密度提高到太赫兹（每秒一万亿周期）和低于20纳米的范围是整个信息处理、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解决，该范式基于超快相干激光泵送石墨烯（一个原子厚，蜂窝状的碳材料）和单壁碳纳米管（卷起的单层石墨烯片）。研究人员将使用可见光谱外的短脉冲太赫兹光和超快相机技术直接监测这些碳纳米材料中光激发态的形成和时间演变。这种新方法将使他们能够在飞秒尺度上捕捉和控制他们的新电磁特性，或者是千万亿分之一秒。该结果将为展示其巨大的发展潜力提供令人着迷的机会，例如，超过千兆赫兹的光调制器，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器件。我们在“超快”和“超小”挑战中的成功，将为开发新一代光电器件揭示尚未发现的物理过程，并为维持信息革命和21世纪的数字经济提供前景。教育是这一提议中不可或缺的组成部分。它包括相互关联的、具体的教育计划，涵盖小规模的大学教授/本科生，针对高中教师和学生的“物理日”计划；向代表性不足的少数族裔学生提供外展服务，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单层石墨烯中的狄拉克费米子是量子和光电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量子过程，并展示其在器件应用中的巨大潜力。主要目标是：确定强光激发单层石墨烯的宽带增益谱和阈值；利用强太赫兹脉冲在狄拉克锥附近演示相干光驱动的带隙打开；研究石墨烯中、远红外极端非线性波混频；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。及时推进的方法在于超短太赫兹脉冲，特别制造的高质量单层和多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的结合。这一提议已经确定了令人信服的机会，以推进当今一些最令人兴奋的材料中最缺乏解决的领域之一，即碳纳米结构的动态，非平衡和非线性方面。目标定位问题涉及到物质的量子光控制、太赫兹电输运和超快光电技术等多个前沿领域。尽管复杂的理论研究已经在进行中，但探索广泛预测的基本现象的实验计划，如所提议的，已经落后了。这些原始结果具有变革性，为基于石墨烯和碳纳米管的超太赫兹调制器、可饱和吸收器、超宽带增益介质的出现开辟了可能性。

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.