Yevgeniy Korniyenko: Nonlinear response of a ballistic graphene transistor with an ac-driven gate: high harmonic generation and THz detection

Yevgeniy Korniyenko, Oleksii Shevtsov, and Tomas Löfwander Department of Microtechnology and Nanoscience - MC2, Chalmers University of Technology, SE-412 96 Göteborg, Sweden We present results for time-dependent electron transport in a ballistic graphene field-effect transistor with an ac-driven gate [1,2]. Nonlinear response to the ac drive is derived utilizing Floquet theory for scattering states in combination with Landauer-Büttiker theory for transport. We identify two regimes that can be useful for applications: (i) low and (ii) high doping of graphene under source and drain contacts, relative to the doping level in the graphene channel, which in an experiment can be varied by a back gate. In both regimes, inelastic scattering induced by the ac drive can excite quasi-bound states in the channel that leads to resonant promotion of higher order sidebands. In regime (i) we observe Fano resonances in the main transmission channel and Breit-Wigner resonances for sidebands. In regime (ii) the channels display double barrier tunneling resonances instead. Already for weak ac drive strength, this leads to a substantial change in the direct current between source and drain. For strong ac drive with frequency Ω, we compute the higher harmonics of frequencies nΩ (n integer) in the source-drain conductance. High harmonics (for instance n = 6) can be selectively enhanced by tuning the doping level in the channel or by tuning the drive strength. We propose that the device operated in the weak-drive regime can be used to detect THz radiation, while in the strong-drive regime it can be used as a frequency multiplier. [1] Y. Korniyenko, O. Shevtsov, and T. Löfwander, Physical Review B 93, 035435 (2016) [2] Y. Korniyenko, O. Shevtsov, and T. Löfwander, arXiv:1606.09036 (2016) Yevgeniy Korniyenko is currently a last year PhD student at Applied Quantum Physics group of Chalmers University of Technology, Sweden. His main focus is in theory of time-dependent quantum transport in low-dimensional materials, continuing the interest he had during bachelor and master studies. He received his B.Sc. degree in Electrophysics from National Chiao Tung University in Taiwan (2009) and M.Sc. degree in Nanoscale Science and Technology from Chalmers University of Technology in Sweden (2011).