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Victor Ryzhii

Publications and source records attributed to Victor Ryzhii.

11 recordsLinked to original sources
arXiv2019

Negative terahertz conductivity at vertical carrier injection in a black-Arsenic-Phosphorus-Graphene heterostructure integrated with a light-emitting diode

We propose and analyze the heterostructure comprising a black-arsenic-phosphorus layer (b-As$_{1-x}$P$_x$L) and a graphene layer (GL) integrated with a light-emitting diode (LED). The integrated b-As$_{1-x}$P$_x$L-GL-LED heterostructure can serve as an active part of the terahertz (THz) laser using the interband radiative transitions in the GL. The feasibility of the proposed concept is enabled by the combination of relatively narrow energy gap in the b-As$_{1-x}$P$_x$L and the proper band alignment with the GL. The operation of the device in question is associated with the generation of the electron-hole pairs by the LED emitted near-infrared radiation in the b-As$_{1-x}$P$_x$L, cooling of the photogenerated electrons and holes in this layer, and their injection into the GL. Since the minimum b-As$_{1-x}$PL energy gap is smaller than the energy of optical phonons in the GL, , the injection into the GL can lead to a relatively weak heating of the two-dimensional electron-hole plasma (2D-EHP) in the GL. At the temperatures somewhat lower than the room temperature, the injection can cool the 2D-EHP. This is beneficial for the interband population inversion in the GL, reinforcement of its negative dynamic conductivity, %in the THz range and the realization of the optical and plasmonic modes lasing supporting the new types of the THz radiation sources.

cond-mat.mes-hall↗
arXiv2018

Comment on "Negative Landau damping in bilayer graphene"

In [Phys. Rev. Lett. vol. 119, p. 133901 (2017)] it was argued that two parallel graphene layers in the presence of electron drift support unstable plasmon modes. Here we show that the predicted plasmon instability is an artifact of errors upon evaluation of graphene polarizability in the presence if electron drift. Crucial role of broken Galilean invariance and spatial dispersion of conductivity for suppression of plasmon instabilities is highlighted.

cond-mat.mes-hall↗
arXiv2018

Auger recombination in Dirac materials: A tangle of many-body effects

The peculiar electron dispersion in Dirac materials makes lowest-order Auger processes prohibited or marginally prohibited by energy and momentum conservation laws. Thus, Auger recombination (AR) in these materials is very sensitive to many-body effects. We incorporate them at the level of the $GW$ approximation into the nonequilibrium Green's functions approach to AR and study the role of dynamic screening, spectrum broadening and renormalization in the case of weakly pumped undoped graphene. We find that incorrect treatment of many-body effects can lead to an order-of-magnitude error in the recombination rate. We show that the AR time weakly (sublinearly) depends on the background dielectric constant, which limits the possibility to control recombination by the choice of substrate. However, the AR time can be considerably prolonged by placing graphene under a metal gate or by introducing a bandgap. With carrier cooling taken into account, our results comply with experiments on photoexcited graphene.

cond-mat.mes-hall↗
arXiv2016

Ultra-compact injection terahertz laser using the resonant inter-layer radiative transitions in multi-graphene-layer structure

The optimization of laser resonators represents a crucial issue for the design of terahertz semiconductor lasers with high gain and low absorption loss. In this paper, we put forward and optimize the surface plasmonic metal waveguide geometry for the recently proposed terahertz injection laser based on resonant radiative transitions between tunnel-coupled grapheme layers. We find an optimal number of active graphene layer pairs corresponding to the maximum net modal gain. The maximum gain increases with frequency and can be as large as ~ 500 cm-1 at 8 THz, while the threshold length of laser resonator can be as small as ~ 50 mkm. Our findings substantiate the possibility of ultra-compact voltage-tunable graphene-based lasers operating at room temperature.

cond-mat.mes-hall↗
arXiv2016

Amplified-reflection plasmon instabilities in grating-gate plasmonic crystals

We identify a possible mechanism of the plasmon instabilities in periodically gated two-dimensional electron systems with a modulated electron density (plasmonic crystals) under direct current. The instability occurs due to the amplified reflection of the small density perturbations from the gated/ungated boundaries under the proper phase matching conditions between the crystal unit cells. Based on the transfer-matrix formalism, we derive the generic dispersion equation for the travelling plasmons in these structures. Its solution in the hydrodynamic limit shows that the threshold drift velocity for the instability can be tuned below the plasmon phase and carrier saturation velocities, and the plasmon increment can exceed the collisional damping rate typical to III-V semiconductors at 77 K and graphene at room temperature.

cond-mat.mes-hall↗
arXiv2016

A Fitting Model for Asymmetric I-V Characteristics of Graphene Field-Effect Transistors for Extraction of Intrinsic Mobilities

A fitting model is developed for accounting the asymmetric ambipolarities in the I-V characteristics of graphene field-effect transistors (G-FETs) with doped channels, originating from the thermionic emission and interband tunneling at the junctions between the gated and access regions. Using the model, the gate-voltage-dependent intrinsic mobility as well as other intrinsic and extrinsic device parameters can be extracted. We apply it to a top-gated G-FET with a graphene channel grown on a SiC substrate and with SiN gate dielectric that we reported previously, and we demonstrate that it can excellently fit its asymmetric I-V characteristic.

cond-mat.mes-hall↗
arXiv2015

Emission and amplification of surface plasmons in resonant - tunneling van der Waals heterostructures

We predict a new mechanism of surface plasmon amplification in graphene-insulator-graphene van der Waals heterostructures. The amplification occurs upon the stimulated interlayer electron tunneling accompanied by the emission of a coherent plasmon. The quantum-mechanical calculations of the non-local high-frequency tunnel conductivity show that a relative smallness of the tunneling exponent can be compensated by a strong resonance due to the enhanced tunneling between electron states with collinear momenta in the neighboring graphene layers. With the optimal selection of the barrier layer, the surface plasmon gain due to the inelastic tunneling can compensate or even exceed the loss due to both Drude and interband absorption. The tunneling emission of the surface plasmons is robust against a slight twist of the graphene layers and might explain the electroluminescence from the tunnel-coupled graphene layers observed in the recent experiments.

cond-mat.mes-hall↗
arXiv2014

Carrier-carrier scattering and negative dynamic conductivity in pumped graphene

We theoretically examine the effect of carrier-carrier scattering processes (electron-hole and electron-electron) on the intraband radiation absorption and their contribution to the net dynamic conductivity in optically or electrically pumped graphene. We demonstrate that the radiation absorption assisted by the carrier-carrier scattering can be stronger than the Drude absorption due to the carrier scattering on disorder. Since the intraband absorption of radiation effectively competes with its interband amplification, this can substantially affect the conditions of the negative dynamic conductivity in the pumped graphene and, hence, the interband terahertz and infrared lasing. We find the threshold values of the frequency and quasi-Fermi energy of nonequilibrium carriers corresponding to the onset of negative dynamic conductivity. The obtained results show that the effect of carrier-carrier scattering shifts the threshold frequency of the radiation amplification in pumped graphene to higher values. In particular, the negative dynamic conductivity is attainable at the frequencies above 6 THz in graphene on SiO2 substrates at room temperature. The threshold frequency can be decreased to markedly lower values in graphene structures with high-k substrates due to screening of the carrier-carrier scattering, particularly at lower temperatures.

cond-mat.mes-hall↗
arXiv2010

Observation of Amplified Stimulated Terahertz Emission from Optically Pumped Epitaxial Graphene Heterostructures

We experimentally observe the fast relaxation and relatively slow recombination dynamics of photogenerated electrons/holes in an epitaxial graphene-on-Si heterostructure under pumping with a 1550-nm, 80-fs pulsed fiber laser beam and probing with the corresponding terahertz (THz) beam generated by and synchronized with the pumping laser. The time-resolved electric-field intensity originating from the coherent terahertz photon emission is electro-optically sampled in total-reflection geometry. The Fourier spectrum from 1.8 to 5.2 THz agrees well the pumping photon spectrum. This result is attributed to amplified emission of THz radiation from the graphene sample stimulated by the THz probe beam, and provides evidence for the occurrence of negative dynamic conductivity in the terahertz spectral range.

cond-mat.mtrl-sci↗
arXiv2008

Device Model for Graphene Nanoribbon Phototransistor

An analytical device model for a graphene nanoribbon phototransistor (GNR-PT) is presented. GNR-PT is based on an array of graphene nanoribbons with the side source and drain contacts, which is sandwiched between the highly conducting substrate and the top gate. Using the developed model, we derive the explicit analytical relationships for the source-drain current as a function of the intensity and frequency of the incident radiation and find the detector responsivity. It is shown that GNR-PTs can be rather effective photodetectors in infrared and terahertz ranges of spectrum.

cond-mat.mes-hall↗