Terahertz Dispersion and Amplification under Electron Streaming in Graphene at 300 K
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INTERNATIONAL SYMPOSIUM “NANOPHYSICS AND NANOELECTRONICS”, NIZHNY NOVGOROD, MARCH 10–13, 2020
Terahertz Dispersion and Amplification under Electron Streaming in Graphene at 300 K A. A. Andronova,* and V. I. Pozdniakovaa a Institute
for Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod, 603950 Russia *e-mail: [email protected] Received April 15, 2019; revised April 21, 2020; accepted April 21, 2020
Abstract—We interpret the recent observations of Otsuji’s team (Sendai) on switching from absorption to amplification at a temperature of T = 300 K during the passage of terahertz radiation through hexagonal boron nitride–graphene sandwiches with multiple gates on the surface with an increase in the electric field in graphene. It is shown that these effects are related to dispersion and negative conductivity near the transittime frequency of electrons in momentum space under streaming (anisotropic distribution) in graphene in a strong electric field. On the basis of these data, a universal tunable terahertz source is proposed, which has the form of a graphene-containing sandwich with a high-resistance silicon wafer (a cavity) with an applied voltage. This terahertz cavity is a complete analog of the microwave generator implemented on an InP chip by Vorobev’s team (St. Petersburg). Keywords: THz radiation, graphene, electron streaming, negative conductivity DOI: 10.1134/S106378262009002X
In study [1], the features of the transmission of terahertz (THz) radiation incident normally onto a multi-gate system formed on the surface of boron nitride–graphene sandwiches were observed upon the excitation of gate plasmons and current passage through graphene under the action of an electric field E. The experimental results reported in [1] are schematically shown in Fig. 1. In zero electric field (E = 0), during the passage of THz radiation, resonance absorption at gate plasmon frequencies is observed; the narrower the gate, the higher the resonance frequency, which fully corresponds to the plasmon frequency (see below). With increasing field E, the plasmon resonance frequencies decrease and then turn to zero in the same field E = E1 for gates of different widths. With a further increase in the field, a sufficiently large region without resonance effects is formed. When the field E exceeds a certain threshold E2 (different for different gate widths), resonance effects arise again and they are accompanied by the amplification of THz radiation. Gate plasmons (hereinafter referred to simply as plasmons) and their excitation by current to create a source of electromagnetic radiation (as well as their use for detection) have been discussed for over two decades, starting from Dyakonov’s and Schur’s studies [2, 3]. However, recent development of this research began with the creation of boron nitride–
graphene sandwiches, in which the mobilities reach more than 50 000 cm2/(V s) and the drift velocities, 7 × 107 cm/s at a temperature of T = 300 K (see, for example, [1, 4, 5]). Discussion and generalization of the
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