石墨烯超材料中的等离子体不稳定性和太赫兹波放大
Plasmonic instabilities and terahertz waves amplification in graphene metamaterials
摘要：
等离子体激元振荡在传统的二维电子气系统中已经被深入研究了40多年，以便在远红外区域找到基于Smith-Purcell效应的真空器件的新替代品。然而，除了多方面的努力，到目前为止，在半导体异质结构中的等离子体激元产生已经非常低效。在这里，我们证明了高迁移率石墨烯超材料的使用，由于其众所周知的更强的光-等离子体耦合相比，半导体材料可以显着提高远红外等离子体放大器和发生器的效率。我们探索电流驱动的等离子体动力学，包括完美的透明度和单层石墨烯结构中的光放大。在宽频率范围内实验观察到石墨烯吸收的电流诱导的完全抑制，随后在室温下对入射的太赫兹辐射进行巨大放大（高达约9%的增益）。这些主动等离子体激元过程由石墨烯器件中相对低的偏置电压触发，导致外部量子效率比主要用于远红外技术的流行的光学到太赫兹转换器件的外部量子效率高约两个数量级。我们的研究结果与石墨烯中等离子体激元的相对低水平的损耗和高度的空间限制相结合，将为广泛的集成高速有源光电子器件开辟途径。
英文摘要：
Plasmon oscillations have been intensively studied for more than forty years in conventional two-dimensional electron gas systems in order to find new alternatives to the vacuum devices based on the Smith-Purcell effect in the far-infrared region. However, beside the multiple endeavors, up to date, the plasmon generation in semiconductor heterostructures has been very inefficient. Here we demonstrate that the use of high mobility graphene metamaterials, due to their well-known stronger light-plasmon coupling compared to semiconductor materials can significantly improve the efficiency of far-infrared plasmonic amplifiers and generators. We explore current-driven plasmon dynamics including perfect transparency and light amplification in monolayer graphene structures. Current-induced complete suppression of the graphene absorption is experimentally observed in a broad frequency range followed by a giant amplification (up to about 9 % gain) of an incoming terahertz radiation at room temperature. These active plasmonic processes are triggered by relatively low bias voltage in the graphene devices leading to external quantum efficiency of about two orders of magnitude higher than those of the popular optical-to-terahertz conversion devices largely used in far-infrared technologies. Our results combined with the relatively low level of losses and high degree of spatial confinement of plasmons in graphene will open pathways for a wide range of integrated high speed active optoelectronics devices.
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