Terahertz radiation from surface plasmon polaritons in graphene
We demonstrate a mechanism that allows direct transformation of the surface plasmon polaritons (SPPs) to terahertz radiation. The SPP is excited electrically on a graphene layer deposited on a dielectric substrate. The condition of this direct transformation is the sheet current in graphene is nonlinear and it requires an dc of 5 kV/cm. The frequency and intensity of the terahertz radiation is tunable by the gate voltage and the dc current. Furthermore, such a nonlinear SPP can give rise to an optical bistabilty in terahertz regime.
Due to the nature of graphene’s conductivity, both TE (transverse electric) and TM (transverse magnetic) modes of surface plasmon polaritons are supported on a graphene sheet. We show that both the intraband optical and interband conductivity in graphene becomes nonlinear under a moderate electrical field and in the far-infrared regime. The energy of surface plasmon polaritons is enhanced and enters the radiation zone of dielectrics. As a result, the surface plasmon polariton can be directly transformed to ration without the need of structural modification. The radiation intensity of an electron beam exited surface plasmon polarition can be two orders of magnitude high than that without a graphene layer. The mechanism opens a possibility of generating high powered and tunable radiation sources in FIR and terahertz regime for imaging and sensing applications. We show that for an opaque incident light on the graphene between two dielectrics, reflectivity exhibits bistability due to the nonlinear coupling of the incident light and the surface plasmon polariton. The transmitted light can be two orders of magnitude stronger than the incident light. Finally, we discuss some recent work in charge dynamics in three dimensional Dirac materials.
1. Tao Zhao, Min Hu, Renbin Zhong, Sen Gong, C. Zhang, and Shenggang Liu, Cherenkov terahertz radiation from graphene surface plasmon polaritons excited by an electron beam, Appl. Phys. Lett. 110, 231102 (2017)
2. S. Huang, M. Sanderson, J. Tian, Q. Chen, F. Wang, C. Zhang, Hot carrier relaxation in three dimensional gapped Dirac semi-metals, J. Phys. D: Appl. Phys. 51, 015101 (2018)
3. C. Zhu, F. Wang, Y. Meng, X. Yuan, F. Xiu, H. Luo, Y. Wang, J. Li, X. Lv, L. He, Y. Xu, J. Liu, C. Zhang, Y. Shi, R. Zhang, and S. Zhu, A robust and tuneable mid-wave infrared optical switch enabled by bulk Dirac fermions, Nature Communications 8, 14111 (2017)
Professor Chao Zhang received his PhD in physics in 1987 from City University of New York, USA. From 1987 to 1989, he was a postdoctoral fellow at Max-Planck-Institute for Solid Research in Stuttgart, Germany, working on quantum magneto-transport in semiconductor nanostructures. From 1989 to 1992, He was a research associate at Canada’s Meson Research Facility in Vancouver, working on quantum coherence and dissipation in solids. From 1993, he has been a tenured faculty member in the School of Physics, University of Wollongong, Australia. Currently he is a senior professor of physics. From 2004-2014, he served as the associate director of the Institute of Superconducting and Electronic Materials. He is a Fellow of Australian Institute of Physics. He is the associate editor of Frontier of Optolelectronics. His research interest is in the areas of quantum transport of nanostructures, terahertz photonics, nonlinear dynamics of semiconductors, graphene and topological insulators. He is an advisory member of the International Organising Committee for Infrared, Millimeter and Terahertz Waves. He received several awards including, JSPS Fellow 2001, Norwegian Research Council Senior Fellow 1996, Australian Academy of Sciences International Award 1999, 2000, 2004.
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