5,020 research outputs found

### Theory of the giant plasmon enhanced second harmonic generation in graphene and semiconductor two-dimensional electron systems

An analytical theory of the nonlinear electromagnetic response of a
two-dimensional (2D) electron system in the second order in the electric field
amplitude is developed. The second-order polarizability and the intensity of
the second harmonic signal are calculated within the self-consistent-field
approach both for semiconductor 2D electron systems and for graphene. The
second harmonic generation in graphene is shown to be about two orders of
magnitude stronger than in GaAs quantum wells at typical experimental
parameters. Under the conditions of the 2D plasmon resonance the second
harmonic radiation intensity is further increased by several orders of
magnitude.Comment: 9 pages, 2 figure

### Nonlinear optical response in gapped graphene

We present a formulation for the nonlinear optical response in gapped
graphene, where the low-energy single-particle spectrum is modeled by massive
Dirac theory. As a representative example of the formulation presented here, we
obtain closed form formula for the third harmonic generation (THG) in gapped
graphene. It turns out that the covariant form of the low-energy theory gives
rise to a peculiar logarithmic singularities in the nonlinear optical spectra.
The universal functional dependence of the response function on dimension-less
quantities indicates that the optical nonlinearity can be largely enhanced by
tuning the gap to smaller values.Comment: http://iopscience.iop.org/0953-8984/labtalk-article/4938

### Reductions of integrable equations on A.III-type symmetric spaces

We study a class of integrable non-linear differential equations related to
the A.III-type symmetric spaces. These spaces are realized as factor groups of
the form SU(N)/S(U(N-k) x U(k)). We use the Cartan involution corresponding to
this symmetric space as an element of the reduction group and restrict generic
Lax operators to this symmetric space. The symmetries of the Lax operator are
inherited by the fundamental analytic solutions and give a characterization of
the corresponding Riemann-Hilbert data.Comment: 14 pages, 1 figure, LaTeX iopart styl

### Propagation of edge magnetoplasmons in semiconductor quantum-well structures

The wavelength and the propagation length of the edge magnetoplasmons,
running along the edge of a two-dimensional electron layer in a semiconductor
quantum-well structure are theoretically studied as a function of frequency,
magnetic field, electron density, mobility, and geometry of the structure. The
results are intended to be used for analysis and optimization of operation of
recently invented quantum-well microwave spectrometers operating at
liquid-nitrogen temperatures (I. V. Kukushkin {\em et al}, Appl. Phys. Lett.
{\bf 86}, 044101 (2005)).Comment: 4 pages, including 4 figures. Accepted for publication in Appl. Phys.
Let

### Quantum Theory of the Third-Harmonic Generation in Graphene

A quantum theory of the third-harmonic generation in graphene is presented.
An analytical formula for the nonlinear conductivity tensor
$\sigma^{(3)}_{\alpha\beta\gamma\delta}(\omega,\omega,\omega)$ is derived.
Resonant maxima of the third harmonic are shown to exist at low frequencies
$\omega\ll E_F/\hbar$, as well as around the frequency $\omega=2E_F/\hbar$,
where $E_F$ is the Fermi energy in graphene. At the input power of a CO$_2$
laser ($\lambda\approx 10$ $\mu$m) of about 1 MW/cm$^2$ the output power of the
third-harmonic ($\lambda\approx 3.3$ $\mu$m) is expected to be $\simeq 50$
W/cm$^2$.Comment: 5 pages, 3 figure

### Graphene-based voltage-tunable coherent terahertz emitter

A portion of the electromagnetic wave spectrum between $\sim 0.1$ and $\sim
10$ terahertz (THz) suffers from the lack of powerful, effective, easy-to-use
and inexpensive emitters, detectors and mixers. We propose a multilayer
graphene -- boron-nitride heterostructure which is able to emit radiation in
the frequency range $\sim 0.1-30$ THz with the power density up to $\sim 0.5$
W/cm$^2$ at room temperature. The proposed device is extremely thin, light,
flexible, almost invisible and may completely cover the needs of science and
technology in the sources of terahertz radiation.Comment: 4 pages, 4 figures, slightly modified version of the previous
submissio

### Reply to Comment on `Theory of microwave-induced zero-resistance states in two-dimensional electron systems' and on `Microwave-induced zero-resistance states and second-harmonic generation in an ultraclean two-dimensional electron gas'

We show that all questions raised in the Comment can be easily answered
within the theory formulated in the commented papers. It is also shown that the
bulk theory promoted by the commenter fails to explain the most important
fundamental features of the discussed phenomenon.Comment: 4 pages, 3 figure

### Influence of optical nonlinearities on plasma waves in graphene

A theory of the nonlinear plasma waves in graphene is developed in the
nonperturbative regime. The influence of strong electric fields on the position
and linewidth of plasma resonances in the far-infrared transmission
experiments, as well as on the wavelength and the propagation length in the
scanning near-field optical microscopy experiments is studied. The theory shows
that the fields of order of a few to a few tens of kV/cm should lead to a red
shift and broadening of plasma resonances in the first type and to a reduction
of the wavelength and the propagation length in the second type of experiments.Comment: 6 pages, 3 figure

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