Article
Physics, Applied
Li Wang, Tsung-Tse Lin, Ke Wang, Hideki Hirayama
Summary: This study investigates the impact of parasitic absorption in the narrow module architecture with only two quantum wells, in the context of terahertz quantum cascade lasers utilizing the nonalignment injection scheme via direct-phonon resonance. The optical gain is found to be limited to small (or negative) values even at low temperatures. To address this issue, a strategy of suppressing parasitic absorption by increasing the injection energy is adopted, resulting in successful lasing at 194 K.
APPLIED PHYSICS LETTERS
(2023)
Article
Materials Science, Multidisciplinary
Ze Zheng, Ying Song, Yu Wei Shan, Wei Xin, Jin Luo Cheng
Summary: We theoretically investigate optical injection processes, including one- and two-photon carrier injection and two-color coherent current injection, in twisted bilayer graphene. By calculating the injection coefficient spectra, we find the significance of interlayer coupling in the injection processes and understand the transitions between different bands.
Article
Multidisciplinary Sciences
Fan Ye, Yiyang Wang, Li Wang, Tsung-Tse Lin, Fantai Zeng, Yue Ji, Jinchuan Zhang, Fengqi Liu, Hideki Hirayama, Ke Wang, Yi Shi, Youdou Zheng, Rong Zhang
Summary: Non-polar m-plane GaN terahertz quantum cascade laser (THz-QCL) structures were studied with two different design schemes: traditional three-well resonant-phonon (RP) scheme and two-well phonon scattering injection (PSI) scheme. The peak gains were calculated using non-equilibrium Green's function calculation, and results showed peak gains of 41.8 cm(-1) at 8.2 THz and 44.2 cm(-1) at 7.7 THz at 300 K for RP and PSI schemes, respectively. The PSI scheme mitigates the broadening effect in GaN due to its configuration. Doping effects on peak gain were analyzed, showing distinct doping density dependence for the two designs. The results suggest the possibility of GaN-based THz-QCL lasing at room temperature.
SCIENTIFIC REPORTS
(2023)
Article
Physics, Applied
Meenhaz Ansari, Subhana Nafees, S. S. Z. Ashraf, Absar Ahmad
Summary: This paper presents a theoretical investigation on the generation of Cerenkov emission of terahertz acoustic phonons in bilayer graphene. The study focuses on the dependencies of phonon emission spectrum and intensity on factors such as phonon frequency, drift velocity, electron temperature, concentration, and emission angle. The results show that the magnitude of the emission spectrum increases at larger drift velocities and applied electric fields, with the peak shifting towards higher frequencies. The study highlights the significance of bilayer graphene in acousto/optoelectronic device applications and high-frequency phonon spectrometers.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Multidisciplinary Sciences
Mir Mohammad Sadeghi, Yajie Huang, Chao Lian, Feliciano Giustino, Emanuel Tutuc, Allan H. MacDonald, Takashi Taniguchi, Kenji Watanabe, Li Shi
Summary: The peculiar electron-phonon interaction in graphene heterostructures enables ultrahigh mobility, electron hydrodynamics, superconductivity, and superfluidity. A peak in the Lorenz ratio near 60 kelvin and its decrease with increased mobility are observed in degenerate graphene, indicating an unusual behavior. This experimental observation, combined with ab initio calculations and analytical models, suggests that broken reflection symmetry in graphene heterostructures can relax the selection rule for electron coupling with flexural phonons, contributing to the increase of the Lorenz ratio at intermediate temperatures.
Article
Nanoscience & Nanotechnology
Vipin Kumar, Pushpendra Kumar
Summary: The relaxation phenomenon of carriers through the scattering of electrons by long-wavelength phonons in suspended monolayer and bilayer graphene is reported to understand the effect of electron-phonon interaction on the anomalous Rabi oscillations. The electron-phonon interaction in monolayer and bilayer graphene does not significantly induce the relaxation of charge carriers, indicating the robustness of anomalous Rabi oscillations near the Dirac point.
PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES
(2022)
Article
Optics
Shiran Levy, Nathalie Lander Gower, Silvia Piperno, Sadhvikas J. Addamane, John L. Reno, Asaf Albo
Summary: We propose a highly diagonal split-well resonant-phonon (SWRP) active region design for GaAs/Al0.3Ga0.7As terahertz quantum cascade lasers (THz-QCLs). The design successfully suppresses thermally activated leakage channels, as evidenced by the observation of negative differential resistance at room temperature. The reduced overlap between the doped region and the active level states improves the performance of the laser.
Article
Materials Science, Multidisciplinary
I. V. Oladyshkin, S. B. Bodrov, A. V. Korzhimanov, A. A. Murzanev, Yu. A. Sergeev, A. I. Korytin, M. D. Tokman, A. N. Stepanov
Summary: The spontaneous optical emission of graphene under intense single-cycle terahertz pulses is investigated experimentally and theoretically. The study reveals that the emitted photons are polarized normally to the electric field of the terahertz pulse, indicating both heating and non-equilibrium momentum distribution. By comparing the measured optical spectrum and polarization anisotropy with numerical modeling, the momentum isotropization time for electrons in graphene is estimated to be around 25 fs, and the time evolution of the distribution function in k space is roughly reconstructed.
Article
Multidisciplinary Sciences
Dehui Zhang, Zhen Xu, Gong Cheng, Zhe Liu, Audrey Rose Gutierrez, Wenzhe Zang, Theodore B. Norris, Zhaohui Zhong
Summary: In this study, the authors propose a new hybrid photoconductive switch design by engineering a hot-carrier fast lane using graphene on silicon. This design allows for a high-speed photoconductive switch without sacrificing the generated power.
NATURE COMMUNICATIONS
(2022)
Review
Nanoscience & Nanotechnology
Taiichi Otsuji, Stephane Albon Boubanga-Tombet, Akira Satou, Deepika Yadav, Hirokazu Fukidome, Takayuki Watanabe, Tetsuya Suemitsu, Alexander A. Dubinov, Vyacheslav V. Popov, Wojciech Knap, Valentin Kachorovskii, Koichi Narahara, Maxim Ryzhii, Vladimir Mitin, Michael S. Shur, Victor Ryzhii
Summary: This paper reviews recent advancements in graphene-based plasmonic metamaterials for terahertz (THz) laser transistors. The researchers investigate various approaches using graphene plasmonic metamaterials to achieve room-temperature, dry-cell-battery operated intense THz lasing with fast direct modulation. The paper discusses device structures and design constraints for coherent light sources applicable to future THz wireless communication systems.
Article
Chemistry, Physical
Chenjing Quan, Xiao Xing, Tingyuan Jia, Zeyu Zhang, Chunwei Wang, Sihao Huang, Zhengzheng Liu, Juan Du, Yuxin Leng
Summary: The charge transfer process in two-dimensional graphene/transition metal dichalcogenides heterostructures was investigated. The study revealed the correlation between the hot phonon bottleneck effect in graphene and the charge transfer process. The existence of interlayer charge transfer in the heterostructure and its dependence on pump fluence were confirmed.
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
(2022)
Article
Chemistry, Multidisciplinary
Minjun Feng, Senyun Ye, Jia Wei Melvin Lim, Yuanyuan Guo, Rui Cai, Qiannan Zhang, Huajun He, Tze Chien Sum
Summary: A thorough understanding of hot-carrier dynamics in halide perovskites is crucial for advancing next generation photovoltaics. Pump-push-probe (PPP) spectroscopy has recently emerged as a powerful tool for studying hot-carrier dynamics, but limited information on initial excitation density and carrier temperature has hindered its full potential. This work presents a unified model that allows the retrieval of these essential hot carrier metrics under the push conditions, enabling direct comparison with traditional pump-probe spectroscopy.
Article
Optics
Alka Mehta, Jyoti Rajput, Niti Kant
Summary: This paper proposes a new scheme to efficiently generate THz radiation by interaction of nonrelativistic lasers with plasma, resulting in efficient THz radiation.
Article
Materials Science, Multidisciplinary
Mohsen Sabbaghi, Tobias Stauber, Hyun-Woo Lee, J. Sebastian Gomez-Diaz, George W. Hanson
Summary: This work investigates the in-plane optical phonon modes of current-carrying single-layer graphene and identifies the effects of DC current on the frequency shifts and the breaking of rotational symmetry.
Article
Physics, Applied
Xiang Li, Tingting Yang, Yangqi Liu, Jingyu Liu, Bin Liu, Longfeng Lv, Yanbing Hou, Yan Zhang, Jingling Shen, Bo Zhang
Summary: The ultrafast carrier response of the perovskite/MoO3/graphene heterostructure was studied using optical-pump terahertz (THz) probe spectroscopy. The high work function of MoO3 changes the tunable graphene Fermi level through hole doping, leading to more negative photoconductivity and enabling ultra-fast THz functional manipulation. Subsequent THz signal decrease is related to hot-carrier cooling and carrier concentration from the CH3NH3PbI3 layer, reducing the positive conductance of the hybrid structure compared to neat CH3NH3PbI3.
JOURNAL OF PHYSICS D-APPLIED PHYSICS
(2021)
Article
Physics, Applied
M. Ryzhii, V Ryzhii, T. Otsuji, V Mitin, M. S. Shur
Summary: The response of lateral n(+)-i-n-n(+) graphene field-effect transistors (GFETs) to terahertz (THz) radiation is analyzed in this study. The nonlinearity caused by Coulomb drag and plasmonic oscillations in the GFET channel enables a resonantly strong response, which can be used for effective resonant detection of THz radiation.
APPLIED PHYSICS LETTERS
(2022)
Article
Optics
Yuma Takida, Kouji Nawata, Takashi Notake, Taiichi Otsuji, Hiroaki Minamide
Summary: A nonlinear optical mixing technique is used to detect and characterize sub-nanosecond terahertz (THz)-wave pulses. The frequency up-conversion and parametric amplification methods are employed for sensitive detection and intensity cross-correlation characterization. The experimental results reveal the temporal profile of THz-wave pulses generated by the injection-seeded THz-wave parametric generator (is-TPG) in the tunable range of 0.95-2.00 THz to have a pulse width of 150-190 ps at full width at half-maximum.
Article
Optics
D. S. Ponomarev, D. Lavrukhin, N. Zenchenko, T. Frolov, I. A. Glinskiy, R. A. Khabibullin, G. M. Katyba, V. N. Kurlov, T. Otsuji, K. Zaytsev
Summary: We present a sapphire-fiber-based lens that enhances the emitted THz power of a large-area photo-conductive antenna (PCA). Numerical simulations demonstrate the effectiveness of the lens in redistributing the photocarriers density in the PCA's gap. We also propose a step-by-step process to precisely and controllably place the sapphire-fiber on the surface of a single PCA.
Article
Multidisciplinary Sciences
Maxim Ryzhii, Elena Ryzhii
Summary: Simplified nonlinear models of biological cells are widely used in computational electrophysiology to reproduce qualitative characteristics of various organs. Compared to complex models, simplified models with few variables and parameters facilitate nonlinear analysis and reduce computational load. This paper investigates the pacemaking variants of two-variable excitable cell models and explores their main nonlinear dynamic features through numerical simulations.
Article
Physics, Applied
V. Ryzhii, T. Otsuji, M. Ryzhii, V. Mitin, M. S. Shur
Summary: This study demonstrates that resonant plasmonic detection significantly enhances the sensitivity of terahertz detectors based on a gated graphene field-effect transistor structure. By utilizing gated p and n regions as hole and electron reservoirs and terahertz resonant plasma cavities, the proposed device achieves terahertz signal rectification and excitation of plasmonic oscillations, leading to a substantial increase in detector responsivity.
PHYSICAL REVIEW APPLIED
(2022)
Article
Physics, Applied
V. Ryzhii, M. Ryzhii, V. Mitin, M. S. Shur, T. Otsuji
Summary: The Zener-Klein interband tunneling in graphene layers can be utilized for processing and generation of terahertz signals, with negative dynamic conductance and transit-time instability. By using periodic cascade structures, THz amplification and radiation can be achieved.
JOURNAL OF APPLIED PHYSICS
(2022)
Article
Optics
Dmitry S. Ponomarev, Denis Lavrukhin, Igor A. Glinskiy, Alexander E. Yachmenev, Nikolay Zenchenko, Rustam A. Khabibullin, Yurii G. Goncharov, Taiichi Otsuji, Kirill I. Zaytsev
Summary: This study proposes the design of a photoconductive antenna (PCA) emitter with a plasmonic grating featuring a very high plasmonic Au electrode with a thickness of 170 nm. Numerical simulations show that increasing h leads to the excitation of higher-order plasmon guided modes in the Au slit waveguides, resulting in an additional increase in the emitted THz power. The fabricated PCA demonstrates efficient operation with low-power laser excitation, achieving an overall THz power of 5.3 mu W over a bandwidth of approximately 4.0 THz, corresponding to a conversion efficiency of 0.2%. This design holds promise for modern THz spectroscopic and high-speed imaging applications.
Article
Optics
Koichi Tamura, Chao Tang, Daichi Ogiura, Kento Suwa, Hirokazu Fukidome, Yuma Takida, Hiroaki Minamide, Tetsuya Suemitsu, Taiichi Otsuji, Akira Satou
Summary: In this study, a new epitaxial graphene field-effect transistor with an asymmetric dual-grating-gate (ADGG) structure was designed and fabricated to achieve fast and sensitive detection of terahertz radiation. The experimental results demonstrated its promising performance in high-speed wireless communication systems.
Article
Physics, Applied
V. Ryzhii, C. Tang, T. Otsuji, M. Ryzhii, V. Mitin, M. S. Shur
Summary: We evaluated THz detectors based on graphene channel (GC) and a floating metal gate (MG) separated from GC by a black-phosphorus (b-P) or black-arsenic (b-As) barrier layer (BL). The operation of these GC-FETs involves heating of the two-dimensional electron gas in GC by THz radiation, leading to thermionic emission of hot electrons from GC to MG. This results in variation of the floating gate potential, affecting the source-drain current. At THz radiation frequencies close to plasmonic resonance frequencies in the gated GC, the variation in source-drain current and detector responsivity can be resonantly large.
JOURNAL OF APPLIED PHYSICS
(2023)
Article
Physiology
Maxim Ryzhii, Elena Ryzhii
Summary: This paper presents a compact and computationally lightweight rabbit AVN model based on the Aliev-Panfilov two-variable cardiac cell model. The model demonstrates broad functionality, including normal sinus rhythm, AVN automaticity, filtering of high-rate atrial rhythms during atrial fibrillation and atrial flutter, and realistic conduction curves in the control case and the cases of FP and SP ablation. The model can be used as a stand-alone module or as a part of complex atrial or whole heart simulation systems, and helps to understand some puzzling functions of AVN.
FRONTIERS IN PHYSIOLOGY
(2023)
Article
Chemistry, Multidisciplinary
Omnia Samy, Mohamed Belmoubarik, Taiichi Otsuji, Amine El Moutaouakil
Summary: This study presents a thin THz absorber that can be easily tuned through the whole THz range (0.1-10 THz) by applying a low gate voltage (<1 V). The structure is based on cheap and abundant materials (MoS2/graphene). The absorptance frequency and width can be controlled by varying the structure and substrate dimensions, making it a promising alternative to expensive THz metamaterial-based absorbers.
Article
Nanoscience & Nanotechnology
V. Ryzhii, C. Tang, T. Otsuji, M. Ryzhii, S. G. Kalenkov, V. Mitin, M. S. Shur
Summary: In this study, we investigate the response of the micromechanical field-effect transistors (MMFETs) to terahertz (THz) signals. The MMFET utilizes microcantilevers (MC) as a floating gate and the movable mirror of Michelson optical interferometer. The mechanical vibrations of MC are converted into optical signals, allowing MMFET to operate as a THz radiation detector. The combination of mechanical and plasmonic resonances in MMFET, along with optical amplification, enables effective THz detection.
