Abstract
We study terahertz (THz) radiation transmission through grating-gate graphene-based nanostructures. We report on room-temperature THz radiation amplification stimulated by current-driven plasmon excitation. Specifically, with an increase of the dc current under periodic charge density modulation, we observe a strong redshift of the resonant THz plasmon absorption, followed by a window of complete transparency to incoming radiation and subsequent amplification and blueshift of the resonant plasmon frequency. Our results are, to the best of our knowledge, the first experimental observation of energy transfer from dc current to plasmons leading to THz amplification. Additionally, we present a simple model offering a phenomenological description of the observed THz amplification. This model shows that in the presence of a dc current the radiation-induced correction to dissipation is sensitive to the phase shift between oscillations of carrier density and drift velocity. And, with an increasing current, the dissipation becomes negative, leading to amplification. The experimental results of this work, as all obtained at room-temperature, pave the way toward the new 2D plasmon-based, voltage-tunable THz radiation amplifiers.
8 More- Received 13 February 2020
- Revised 7 May 2020
- Accepted 20 May 2020
DOI:https://doi.org/10.1103/PhysRevX.10.031004
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
More than 40 years ago, a new direction in physics opened up with the arrival of plasma wave electronics. The possibility that plasma waves could propagate faster than electrons fascinated all, suggesting that so-called “plasmonic” devices could work at terahertz (THz) frequencies, too high for standard electronic devices. However, numerous experimental attempts to realize such amplifiers or emitters failed, and the creation of compact, tunable, room-temperature THz devices remains a challenge. To that end, we explore THz light-plasmon coupling, light absorption, and amplification in a graphene-based system, whose excellent room-temperature electrical and optical properties are ideal for solving this problem.
Using monolayer graphene grating-gate structures, we demonstrate tunable resonant plasmon absorption which, with an increase of the current, turns to THz radiation amplification. The observed gain of up to 9% is far beyond the well-known landmark level of 2.3% that is maximal available in monolayer graphene when photons directly interact with electrons. To interpret our results, we use a dissipative plasmonics crystal model, which captures the main trends and basic physics of the amplification phenomena. Specifically, the model predicts that increasing current drives the system into an amplification regime, wherein the plasma waves may transfer energy to the incoming electromagnetic waves.
All results were obtained at room temperature. Therefore, our experimental setup paves the way toward future THz plasmonic technology with a new generation of all-electronic, resonant, voltage-controlled THz amplifiers.