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Interpretation of the Transition from Absorption to Amplification in an Electric Field of Resonant Terahertz Reflection in Graphene Sandwiches and Prospects for Creating a Universal Terahertz Sandwich Laser.

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Title: Interpretation of the Transition from Absorption to Amplification in an Electric Field of Resonant Terahertz Reflection in Graphene Sandwiches and Prospects for Creating a Universal Terahertz Sandwich Laser.
Authors: Andronov, A. A.1 (AUTHOR) andron@ipmras.ru, Pozdnyakova, V. I.1 (AUTHOR)
Source: JETP Letters. Jun2026, Vol. 123 Issue 11, p749-755. 7p.
Subjects: Terahertz technology, Wave amplification, Frequency tuning, Electric field effects, Fermions, Electronic excitation, Submillimeter waves
Abstract: The performed calculations and discussions have explained the mechanisms of terahertz radiation reflection from high-quality graphene sandwiches (coated with hexagonal boron nitride layers) with stripline resonators and an electric field and current in graphene in an experiment carried out by the group led by Taiichi Otsuji. In that experiment, a decrease in the frequency and the suppression of terahertz resonances in the strips to their disappearance were observed with an initial increase in the field strength and the emergence of resonances with increasing frequency and amplification was observed in high fields. It is demonstrated in this work that resonance suppression in low fields is caused by the Dirac relation between the electron velocity and the momentum in graphene and by diffusional heating of electrons with increasing temperature. The emergence of resonances with amplification in high fields is caused by the transition to dynamic heating (streaming) of electrons in graphene, where the main electron dynamic processes are motion in the electric field and the emission of optical phonons. Our calculations show that a negative terahertz conductivity (with frequencies dependent on the electric field) and a positive additive to the real part of the graphene response with a region where it increases with the frequency arise in graphene under these conditions. This leads to the observed increase in resonance frequencies with the field and amplification at the resonances. These observations and our analysis provide a realistic basis for creating a cw terahertz laser at room temperature, tunable in frequency by an electric field over a wide range (1–10 THz), based on such sandwiches, without stripline resonators. [ABSTRACT FROM AUTHOR]
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Abstract:The performed calculations and discussions have explained the mechanisms of terahertz radiation reflection from high-quality graphene sandwiches (coated with hexagonal boron nitride layers) with stripline resonators and an electric field and current in graphene in an experiment carried out by the group led by Taiichi Otsuji. In that experiment, a decrease in the frequency and the suppression of terahertz resonances in the strips to their disappearance were observed with an initial increase in the field strength and the emergence of resonances with increasing frequency and amplification was observed in high fields. It is demonstrated in this work that resonance suppression in low fields is caused by the Dirac relation between the electron velocity and the momentum in graphene and by diffusional heating of electrons with increasing temperature. The emergence of resonances with amplification in high fields is caused by the transition to dynamic heating (streaming) of electrons in graphene, where the main electron dynamic processes are motion in the electric field and the emission of optical phonons. Our calculations show that a negative terahertz conductivity (with frequencies dependent on the electric field) and a positive additive to the real part of the graphene response with a region where it increases with the frequency arise in graphene under these conditions. This leads to the observed increase in resonance frequencies with the field and amplification at the resonances. These observations and our analysis provide a realistic basis for creating a cw terahertz laser at room temperature, tunable in frequency by an electric field over a wide range (1–10 THz), based on such sandwiches, without stripline resonators. [ABSTRACT FROM AUTHOR]
ISSN:00213640
DOI:10.1134/S0021364025610437