Abstract-Giant amplification of terahertz plasmons in a double-layer graphene

M Yu Morozov, I M Moiseenko,  V V Popov

https://iopscience.iop.org/article/10.1088/1361-648X/aaa648/meta

The amplification of terahertz plasmons in a pair of parallel active graphene monolayers is studied theoretically. The plasmon wave in a symmetric double-layer graphene structure splits into two branches with a symmetric and an antisymmetric distribution of tangential to graphene component of the electric field across the plane of symmetry of the structure. It is shown that, normalized to the wavelength, the terahertz plasmon amplification factor of the symmetric mode in the double-layer graphene structure could be greater than that in a single graphene layer by four orders of magnitude.

Abstract-Giant amplification of terahertz plasmons in a double-layer graphene

Mikhail Morozov,  Ilya Moiseenko,  Vyacheslav Popov,

http://iopscience.iop.org/article/10.1088/1361-648X/aaa648/pdf

Amplification of terahertz plasmons in a pair of parallel active graphene monolayers is studied theoretically. Plasmon wave in symmetric double-layer graphene structure splits into two branches with a symmetric and an antisymmetric distribution of tangential to graphene component of the electric field across the plane of symmetry of the structure. It is shown that normalized to the wavelength terahertz plasmon amplification factor of the symmetric mode in the double-layer graphene structure could be greater than that in a single graphene layer by 4 orders of magnitude.

Abstract-A model for terahertz plasmons in graphene

·         A. G. Every, R. Warmbier , A. Quandt

http://link.springer.com/article/10.1007/s11082-015-0370-4

We derive and analyze a 2D model for plasmons, in order to understand the general preconditions for the appearance of THz plasmons in low-dimensional nanosystems like graphene. Using experimental data and back of the envelope type calculations, we discuss the typical frequency ranges of plasmon resonances in such systems. Next we compare our results to recent ab initio calculations for ideal graphene, and show that these are consistent with the predictions of a 3D plasmon model, rather than a 2D model. The validity of the ab initio calculation does not extend to long-wavelength regime where our 2D model holds.

Abstract-The effect of beam pre-bunching on the excitation of terahertz plasmons in a parallel plane guiding system

Suresh C. Sharma¹ and Pratibha Malik¹
 http://scitation.aip.org/content/aip/journal/pop/22/4/10.1063/1.4916765?TRACK=RSS
1 Department of Applied Physics, Delhi Technological University (DTU), Shahbad Daulatpur, Bawana Road, Delhi-110042, India
Phys. Plasmas 22, 043301 (2015); http://dx.doi.org/10.1063/1.4916765

The excitation of terahertz (THz) plasmons by a pre-bunched relativistic electron beam propagating in a parallel plane semiconducting guiding system is studied. It is found that the n-InSb semiconductor strongly supports the confined surface plasmons in the terahertz frequency range. The growth rate and efficiency of the THz surface plasmons increase linearly with modulation index and show the largest value as modulation index approaches unity. Moreover, the growth rate of the instability scales as one-third power of the beam density and inverse one-third power of the THz radiation frequency.

Abstract-Damping of Terahertz Plasmons in Graphene Coupled with Surface Plasmons in Heavily-Doped Substrate

A. Satou, Y. Koseki, V. Ryzhii, V. Vyurkov, T. Otsuji

(Submitted on 15 Jan 2014)

http://arxiv.org/abs/1401.3396

Coupling of plasmons in graphene at terahertz (THz) frequencies with surface plasmons in a heavily-doped substrate is studied theoretically. We reveal that a huge scattering rate may completely damp out the plasmons, so that proper choices of material and geometrical parameters are essential to suppress the coupling effect and to obtain the minimum damping rate in graphene. Even with the doping concentration 10^{19} - 10^{20} cm^{-3} and the thickness of the dielectric layer between graphene and the substrate 100 nm, which are typical values in real graphene samples with a heavily-doped substrate, the increase in the damping rate is not negligible in comparison with the acoustic-phonon-limited damping rate. Dependence of the damping rate on wavenumber, thicknesses of graphene-to-substrate and gate-to-graphene separation, substrate doping concentration, and dielectric constants of surrounding materials are investigated. It is shown that the damping rate can be much reduced by the gate screening, which suppresses the field spread of the graphene plasmons into the substrate.

Abstract-Terahertz Magnetoplasmon Energy Concentration and Splitting in Graphene PN Junctions

Nima Chamanara, Dimitrios L. Sounas, Thomas Szkopek, Christophe Caloz

http://arxiv.org/abs/1306.5425

(Submitted on 23 Jun 2013)

Terahertz plasmons and magnetoplasmons propagating along electrically and chemically doped graphene p-n junctions are investigated. It is shown that such junctions support non-reciprocal magnetoplasmonic modes which get concentrated at the middle of the junction in one direction and split away from the middle of the junction in the other direction under the application of an external static magnetic field. This phenomenon follows from the combined effects of circular birefringence and carrier density non-uniformity. It can be exploited for the realization of plasmonic isolators.

Abstract-Significant performance enhancement in photoconductive terahertz optoelectronics by incorporating plasmonic contact electrodes

My Note: This is the Abstract which has just appeared online this morning, relating to the recent news out of the University of Michigan.

• C.W. Berry,
• N. Wang,
• M.R. Hashemi,
• M. Unlu
• & M. Jarrahi

• http://www.nature.com/ncomms/journal/v4/n3/full/ncomms2638.html

Even though the terahertz spectrum is well suited for chemical identification, material characterization, biological sensing and medical imaging, practical development of these applications has been hindered by attributes of existing terahertz optoelectronics. Here we demonstrate that the use of plasmonic contact electrodes can significantly mitigate the low-quantum efficiency performance of photoconductive terahertz optoelectronics. The use of plasmonic contact electrodes offers nanoscale carrier transport path lengths for the majority of photocarriers, increasing the number of collected photocarriers in a subpicosecond timescale and, thus, enhancing the optical-to-terahertz conversion efficiency of photoconductive terahertz emitters and the detection sensitivity of photoconductive terahertz detectors. We experimentally demonstrate 50 times higher terahertz radiation powers from a plasmonic photoconductive emitter in comparison with a similar photoconductive emitter with non-plasmonic contact electrodes, as well as 30 times higher terahertz detection sensitivities from a plasmonic photoconductive detector in comparison with a similar photoconductive detector with non-plasmonic contact electrodes.

Abstract-Terahertz plasmon amplification using two-dimensional electron-gas layers

Mohammad Ali Khorrami, Samir El-Ghazaly, Shui-Qing Yu, and Hameed Naseem Department of Electrical Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA 

In this study, we present an analytical model to investigate the possibility of guiding and amplifying terahertz (THz) plasmons in a two dimensional electron gas (2DEG) layer of a hetero-structure by applying a bias electric field. This analytical model solves Maxwell equations and semi-classical electronic transport equations inside the biased hetero-structure simultaneously. It is shown that the two dimensional plasmon’s properties alter vastly as the electrons are accelerated by the bias field. Four asymmetric plasmonic modes can propagate inside the un-gated 2DEG layer of the biased hetero-structure. One of these modes in the un-gated 2DEG layer is a growing mode which can be useful in the implementation of THz amplifiers. Since the modes characteristics can be controlled via biasing, design of new plasmonic devices such as modulators and switches is possible by this approach. Similar analysis has been performed in a gated 2DEG layer that shows clear changes in the two dimensional plasmon properties due to the biasing. Unlike the un-gated 2DEG layer, our efforts to find a growing mode in the gated 2DEG layer have failed. These multi-physics models lead to a better understanding of THz plasmonic sources and detectors as well as proposals on new plasmonic devices. Besides, they provide a physical insight into the electron-wave interactions inside the biased hetero-structure.

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