arXiv subjects
Publications and source records attributed to N. A. Savostianova.
Graphene is a two-dimensional material with strongly nonlinear electrodynamics and optical properties. We present some of our recent theoretical results on the quantum and non-perturbative quasi-classical theories of nonlinear effects in graphene, influence of substrates on graphene nonlinearities, plasma oscillations in graphene in the nonlinear regime and other effects.
We consider a periodic array of graphene nanoribbons under the action of a strong dc electric field $E_0$ and an external electromagnetic excitation with the frequency $ω$ and the lateral wave vector $q$. Solving the quasi-classical Boltzmann kinetic equation and calculating the surface dynamic conductivity $σ_{2D}(q,ω,E_0)$ and the absorption coefficient of such a system we show that the real part of the conductivity and the absorption coefficient may become negative under certain conditions. Physically this corresponds to the amplification of the electromagnetic waves at the expense of the energy of the direct current source. The results are discussed in connection with experiments on the surface acoustic waves and on the Smith-Purcell-type graphene-based terahertz emitter.
Graphene is an atomically thin two-dimensional material demonstrating strong optical nonlinearities including harmonics generation, four wave mixing, Kerr and other nonlinear effects. In this paper we theoretically analyze the optical heterodyne detection (OHD) technique of measuring the optical Kerr effect (OKE) in two-dimensional crystals and show how to relate the quantities measured in such experiments with components of the third-order conductivity tensor $σ^{(3)}_{αβγδ}(ω_1,ω_2,ω_3)$ of the two-dimensional crystal. Using results of a recently developed quantum theory of the third-order nonlinear electrodynamic response of graphene we analyze the frequency, charge carrier density, temperature and other dependencies of the OHD-OKE response of this material. We compare our results with a recent OHD-OKE experiment in graphene and find good agreement between the theory and experiment.
We present a degenerate four-wave mixing experiment on a silicon nitride (SiN) waveguide covered with gated graphene. We observe strong dependencies on signal-pump detuning and Fermi energy, i.e. the optical nonlinearity is demonstrated to be electrically tunable. In the vicinity of the interband absorption edge ($2|E_F|\approx \hbarω$) a peak value of the waveguide nonlinear parameter of $\approx$ 6400 m$^{-1}$W$^{-1}$, corresponding to a graphene nonlinear sheet conductivity $|σ_s^{(3)}|\approx4.3\cdot 10^{-19}$ A m$^2$V$^{-3}$ is measured.
Graphene is a nonlinear material which can be used as a saturable absorber, frequency mixer and frequency multiplier. We investigate the third harmonic generation from graphene lying on different substrates, consisting of a dielectric (dispersionless or polar), metalized or non-metalized on the back side. We show that the third harmonic intensity emitted from graphene lying on a substrate, can be increased by orders of magnitude as compared to the isolated graphene, due the LO-phonon resonances in a polar dielectric or due to the interference effects in the substrates metalized on the back side. In some frequency intervals, the presence of the polar dielectric substrate compensates the strongly decreasing with $ω$ frequency dependence of the third-order conductivity of graphene making the response almost frequency independent.
Graphene was shown to have strongly nonlinear electrodynamic properties. In particular, being irradiated by an electromagnetic wave with the frequency $ω$, it can efficiently generate higher frequency harmonics. Here we predict that in a specially designed structure "graphene -- dielectric -- metal" the third-harmonic ($3ω$) intensity can be increased by more than two orders of magnitude as compared to an isolated graphene layer.
Electromagnetic response of a finite-width two-dimensional electron stripe with attached metallic side contacts is theoretically studied. It is shown that contacts substantially influence the position, the linewidth, and the amplitude of plasmon-polariton resonances in the stripe. In finite magnetic fields, absorption of the wave with the inactive circular polarization (which is not absorbed in an infinite system without contacts) may become larger than that of the wave with the active polarization. The results are discussed in view of recent microwave experiments in two-dimensional electron systems.
In the preprint cond-mat/0408050 M. V. Cheremisin noticed that some results (namely Fig. 4) of our recent work (cond-mat/0407364) have been taken from his paper cond-mat/0405176. As clear from the caption to Fig. 4 as well as from the text of our paper, we did not consider the curves shown in that Figure as our original results, but emphasized that they have been obtained in the well known paper Chiu and Quinn, Phys. Rev. B 9, 4724 (1974) 30 years ago. It is a surprise, that M. V. Cheremisin presents the 30-years-old results of Chiu and Quinn as his own results, obtained for the first time in cond-mat/0405176.
Electromagnetic response of a finite-width two-dimensional electron stripe is theoretically studied. It is shown that retardation and radiative effects substantially modify the absorption spectrum of the system at microwave frequencies, leading to a non-trivial zigzag behavior of the magnetoplasmon-polariton modes in magnetic fields, similar to that recently observed by Kukushkin et al. [Phys. Rev. Lett. {\bf 90}, 156801 (2003)].
Magnetic field usually leads to a polarization of electron spins. It is shown that in a system of {\em strongly interacting} particles applying magnetic field may lead to an opposite effect -- depolarization of electron spins. Results of the work are based on an exact-diagonalization study of quantum-dot lithium -- a system of three Coulomb interacting two-dimensional electrons in a parabolic confinement potential.