arXiv subjects

V. Vyurkov

Publications and source records attributed to V. Vyurkov.

13 recordsLinked to original sources

arXiv2016

Abrupt current switching in graphene bilayer tunnel transistors enabled by van Hove singularities

In a continuous search for the energy-efficient electronic switches, a great attention is focused on tunnel field-effect transistors (TFETs) demonstrating an abrupt dependence of the source-drain current on the gate voltage. Among all TFETs, those based on one-dimensional (1D) semiconductors exhibit the steepest current switching due to the singular density of states near the band edges, though the current in 1D structures is pretty low. In this paper, we propose a TFET based on 2D graphene bilayer which demonstrates a record steep subthreshold slope enabled by van Hove singularities in the density of states near the edges of conduction and valence bands. Our simulations show the accessibility of 3.5 x 10$^4$ ON/OFF current ratio with 150 mV gate voltage swing, and a maximum subthreshold slope of (20 μV/dec)$^{-1}$ just above the threshold. The high ON-state current of 0.8 mA/μm is enabled by a narrow (~ 0.3 eV) extrinsic band gap, while the smallness of the leakage current is due to an all-electrical doping of the source and drain contacts which suppresses the band-tailing and trap-assisted tunneling.

cond-mat.mes-hall↗

arXiv2014

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

Coupling of plasmons in graphene at terahert (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.

cond-mat.mes-hall↗

arXiv2013

Hydrodynamic electron transport and nonlinear waves in graphene

We derive the system of hydrodynamic equations governing the collective motion of massless fermions in graphene. The obtained equations demonstrate the lack of Galilean- and Lorentz invariance, and contain a variety of nonlinear terms due to quasi-relativistic nature of carriers. Using those equations, we show the possibility of soliton formation in electron plasma of gated graphene. The quasi-relativistic effects set an upper limit for soliton amplitude, which marks graphene out of conventional semiconductors. The lack of Galilean and Lorentz invariance of hydrodynamic equations is revealed in spectra of plasma waves in the presence of steady flow, which no longer obey the relations of Doppler shift. The possibility of plasma wave excitation by direct current in graphene channels is also discussed.

cond-mat.mes-hall↗

arXiv2013

Double injection in graphene p-i-n structures

We study the processes of the electron and hole injection (double injection) into the i-region of graphene-layer and multiple graphene-layer p-i-n structures at the forward bias voltages. The hydrodynamic equations governing the electron and hole transport in graphene coupled with the two-dimensional Poisson equation are employed. Using analytical and numerical solutions of the equations of the model, we calculate the band edge profile, the spatial distributions of the quasi-Fermi energies, carrier density and velocity, and the current-voltage characteristics. In particular, we demonstrated that the electron and hole collisions can strongly affect these distributions. The obtained results can be used for the realization and optimization of graphene-based injection terahertz and infrared lasers.

cond-mat.mes-hall↗

arXiv2012

Voltage-controlled surface plasmon-polaritons in double graphene layer structures

We study the spectra and damping of surface plasmon-polaritons in double graphene layer structures. It is shown that application of bias voltage between layers shifts the edge of plasmon absorption associated with the interband transitions. This effect could be used in efficient plasmonic modulators. We reveal the influence of spatial dispersion of conductivity on plasmonic spectra and show that it results in the shift of cutoff frequency to the higher values.

cond-mat.mes-hall↗

arXiv2012

Hydrodynamic model for electron-hole plasma in graphene

We propose a hydrodynamic model describing steady-state and dynamic electron and hole transport properties of graphene structures which accounts for the features of the electron and hole spectra. It is intended for electron-hole plasma in graphene characterized by high rate of intercarrier scattering compared to external scattering (on phonons and impurities), i.e., for intrinsic or optically pumped (bipolar plasma), and gated graphene (virtually monopolar plasma). We demonstrate that the effect of strong interaction of electrons and holes on their transport can be treated as a viscous friction between the electron and hole components. We apply the developed model for the calculations of the graphene dc conductivity, in particular, the effect of mutual drag of electrons and holes is described. The spectra and damping of collective excitations in graphene in the bipolar and monopolar limits are found. It is shown that at high gate voltages and, hence, at high electron and low hole densities (or vice-versa), the excitations are associated with the self-consistent electric field and the hydrodynamic pressure (plasma waves). In intrinsic and optically pumped graphene, the waves constitute quasineutral perturbations of the electron and hole densities (electron-hole sound waves) with the velocity being dependent only on the fundamental graphene constants.

cond-mat.mes-hall↗

arXiv2009

Quantum computing based on space states without charge transfer

An implementation of a quantum computer based on space states in double quantum dots is discussed. There is no charge transfer in qubits during calculation, therefore, uncontrollable entan-glement between them due to long-range Coulomb interaction is suppressed. Other plausible sources of decoherence caused by interaction with phonons and gates could be substantially suppressed in the structure too. We also demonstrate how all necessary quantum logic operations, initialization, writing, and read-out could be carried out in the computer.

quant-ph↗

arXiv2008

Effect of Coulomb scattering on graphene conductivity

The effect of Coulomb scattering on graphene conductivity in field effect transistor structures is discussed. Inter-particle scattering (electron-electron, hole-hole, and electron-hole) and scattering on charged defects are taken into account in a wide range of gate voltages. It is shown that an intrinsic conductivity of graphene (purely ambipolar system where both electron and hole densities exactly coincide) is defined by strong electron-hole scattering. It has a universal value independent of temperature. We give an explicit derivation based on scaling theory. When there is even a small discrepancy in electron and hole densities caused by applied gate voltage the conductivity is determined by both strong electron-hole scattering and weak external scattering: on defects or phonons. We suggest that a density of charged defects (occupancy of defects) depends on Fermi energy to explain a sub-linear dependence of conductivity on a fairly high gate voltage observed in experiments. We also eliminate contradictions between experimental data obtained in deposited and suspended graphene structures regarding graphene conductivity.

cond-mat.mes-hall↗

arXiv2008

Non-demolishing measurement of a spin qubit state via Fano resonance

Fano resonances are proposed to perform a measurement of a spin state (whether it is up or down) of a single electron in a quantum dot via a spin-polarized current in an adjacent quantum wire. Rashba-like spin-orbit interaction in a quantum dot prohibits spin-flip events (Kondo-like phenomenon). That ensures the measurement to be non-demolishing.

quant-ph↗

arXiv2008

Why graphene conductivity is constant: scaling theory consideration

In the recent paper [arXiv:0802.2216, 15 Feb 2008], Kashuba argued that the intrinsic conductivity of graphene independent of temperature originated in strong electron-hole scattering. We propose a much more explicit derivation based on a scaling theory approach. We also give an explanation of a rapid increase in graphene conductivity caused by applied gate voltage.

cond-mat.mes-hall↗

arXiv2003

Pseudo-gap and spin polarization in a two-dimensional electron gas

Tunnelling density of states in the vicinity of Fermi level of a two-dimensional electron gas subjected to an external parallel and zeroth magnetic field is calculated. It reveals a pseudo-gap recently observed in the experiments. The gap originates in spin polarization of 2DEG. Non-monotonic dependence of energy on a Landau level filling factor (density) was obtained. It implies the tunneling current peculiarities at filling factors 1/2 and 1. The Ising-like model of the exchange interaction in 2DEG was exploited instead of the conventional one. It was crucial to achieve even a qualitative agreement with experimental data.

cond-mat.str-el↗

arXiv2003

Absolute Negative Conductivity in Two-Dimensional Electron Systems Associated with Acoustic Scattering Stimulated by Microwave Radiation

We discuss the feasibility of absolute negative conductivity (ANC) in two-dimensional electron systems (2DES) stimulated by microwave radiation in transverse magnetic field. The mechanism of ANC under consideration is associated with the electron scattering on acoustic piezoelectric phonons accompanied by the absorption of microwave photons. It is demonstrated that the dissipative components of the 2DES dc conductivity can be negative ($σ_{xx} = σ_{yy} < 0$) when the microwave frequency $Ω$ is somewhat higher than the electron cyclotron frequency $Ω_c$ or its harmonics. The concept of ANC associated with such a scattering mechanism can be invoked to explain the nature of the occurrence of zero-resistance ``dissipationless'' states observed in recent experiments.

cond-mat.mes-hall↗

arXiv2001

Spontaneous Magnetization of a Two-Dimensional Electron Gas

Spontaneous magnetization of a two-dimensional electron gas (2DEG) is discussed. It takes place for sufficiently high electron density (i.e. for a quantum fluid state) with $r_s<10$ which is quite beyond the condition of Wigner crystallization $(r_s>37)$ obtained by Tanatar and Ceperley. The effect essentially depends upon screening and disorder . The energy interval under the Fermi level where a spin polarization occurs as a function of electron density is computed. The spontaneous magnetic moment and a decrease of electron density of states (pseudo-gap) at the Fermi level are found.

cond-mat.str-el↗