Mixing In Graphene Research Articles

Efficient high-harmonic generation in graphene with two-color laser field at orthogonal polarization

High-order frequency mixing in graphene using a two-color radiation field consisting of the fundamental and the second harmonic fields of an ultrashort linearly polarized laser pulse is studied. It is shown that the harmonics originated from the interband transitions are efficiently generated in the case of the orthogonally polarized two-color field. In this case, the generated high-harmonics are stronger than those obtained in the parallel polarization case by more than two orders of magnitude. This is in sharp contrast with the atomic and semiconductor systems, where parallel polarization case is more preferable. The physical origin of this enhancement is also deduced from the three-step semi-classical electron-hole collision model, extended to graphene with pseudo-relativistic energy dispersion. In particular, we discuss the influence of the many particle Coulomb interaction on the HHG process within dynamical Hartree-Fock approximation. Our analysis shows that in all cases we have an overall enhancement of the HHG signal compared with the free-charged carrier model due to the electron-hole attractive interaction.

On the mixing of graphene and oleic acid in kerosene: a dissipative particle dynamics study

On the mixing of graphene and oleic acid in kerosene: a dissipative particle dynamics study

Spin-orbit coupling in elemental two-dimensional materials

The fundamental spin-orbit coupling and spin mixing in graphene and rippled honeycomb lattice materials silicene, germanene, stanene, blue phosphorene, arsenene, antimonene, and bismuthene is investigated from first principles. The intrinsic spin-orbit coupling in graphene is revisited using multi-band $k\cdot p$ theory, showing the presence of non-zero spin mixing in graphene despite the mirror symmetry. However, the spin mixing itself does not lead to the the Elliott-Yafet spin relaxation mechanism, unless the mirror symmetry is broken by external factors. For other aforementioned elemental materials we present the spin-orbit splittings at relevant symmetry points, as well as the spin admixture $b^2$ as a function of energy close to the band extrema or Fermi levels. We find that spin-orbit coupling scales as the square of the atomic number Z, as expected for valence electrons in atoms. For isolated bands, it is found that $b^2\sim Z^4$. The spin-mixing parameter also exhibits giant anisotropy which, to a large extent, can be controlled by tuning the Fermi level. Our results for $b^2$ can be directly transferred to spin relaxation time due to the Elliott-Yafet mechanism, and therefore provide an estimate of the upper limit for spin lifetimes in materials with space inversion center.

Unsteady Flow of Carreau Fluid in a Suspension of Dust and Graphene Nanoparticles With Cattaneo–Christov Heat Flux

Abstract This is a theoretical exploration of the magnetohydrodynamic Carreau fluid in a suspension of dust and graphene nanoparticles. Graphene is a two-dimensional single-atom thick carbon nanosheet. Due to its high thermal conductivity, electron mobility, large surface area, and stability, it has remarkable material, electrical, optical, physical, and chemical properties. In this study, a simulation is performed by mixing of graphene + water and graphene + ethylene glycol into dusty non-Newtonian fluid. Dispersion of graphene nanoparticles in dusty fluids finds applications in biocompatibility, bio-imaging, biosensors, detection and cancer treatment, in monitoring stem cells differentiation, etc. Graphene + water and graphene + ethylene glycol mixtures are significant in optimizing the heat transport phenomena. Initially arising set of physical governing partial differential equations are transformed to ordinary differential equations (ODEs) with the assistance of similarity transformations. Consequential highly nonlinear ODEs are solved numerically through Runge–Kutta Fehlberg scheme. The computational results for nondimensional temperature and velocity profiles are presented through graphs. Additionally, the numerical values of friction factor and heat transfer rate are tabulated numerically for various physical parameter obtained. We also validated the present results with previous published study and found to be highly satisfactory. The formulated model in this study reveals that heat transfer rate and wall friction is higher in mixture of graphene + ethylene glycol when compared to graphene + water.

Frequency-degenerate phase-sensitive optical parametric amplification based on four-wave mixing in graphene–silicon slot waveguide

The phase-sensitive amplification process of a hybrid graphene–silicon (HyGS) slot waveguide with trilayers of graphene is investigated in this paper. Numerical simulation shows that a relatively high extinction ratio (42 dB) is achieved, because of the ultrahigh nonlinear coefficients, with a waveguide length of only 680 µm. In addition, the graphene layer provides the possibility of modulating the phase status and gain of the output signal. This study is expected to be highly beneficial to applications such as integrated optics and graphene-related active optical devices.

Terahertz super-resolution imaging using four-wave mixing in graphene

A perfect lens made from negative refraction (NR) materials is utilized to overcome the diffraction limit. However, these NR lenses are realized by metamaterials, which suffer from high losses, and the volume is bulky. In this Letter, we propose a terahertz NR lens by using a four-wave mixing (FWM) process in graphene. NR is demonstrated because of the phase matching along the surface of graphene. Evanescent waves that store high spatial frequency information can be converted into propagating waves in the nonlinear NR process. An image with subwavelength resolution is reconstructed at the FWM wavelength. Theoretical analysis and numerical simulations are performed to demonstrate the capability of such imaging. The lens has a subwavelength resolution of around λ/5. The lens needs low field intensity due to the strong nonlinear response of graphene in the terahertz frequency. This Letter may have applications in terahertz microscopy.

Multi-frequency sound production and mixing in graphene

The ability to generate, amplify, mix and modulate sound in one simple electronic device would open up a new world in acoustics. Here we show how to build such a device. It generates sound thermoacoustically by Joule heating in graphene. A rich sonic palette is created by controlling the composition and flow of the electric current through the graphene. This includes frequency mixing (heterodyning), which results exclusively from the Joule mechanism. It also includes shaping of the sound spectrum by a dc current and modulating its amplitude with a transistor gate. We show that particular sounds are indicators of nonlinearity and can be used to quantify nonlinear contributions to the conduction. From our work, we expect to see novel uses of acoustics in metrology, sensing and signal processing. Together with the optical qualities of graphene, its acoustic capabilities should inspire the development of the first combined audio-visual nanotechnologies.

Graphene Near-Degenerate Four-Wave Mixing for Phase Characterization of Broadband Pulses in Ultrafast Microscopy

We investigate near-degenerate four-wave mixing in graphene using femtosecond laser pulse shaping microscopy. Intense near-degenerate four-wave mixing signals on either side of the exciting laser spectrum are controlled by amplitude and phase shaping. Quantitative signal modeling for the input pulse parameters shows a spectrally flat phase response of the near-degenerate four-wave mixing due to the linear dispersion of the massless Dirac Fermions in graphene. Exploiting these properties we demonstrate that graphene is uniquely suited for the intrafocus phase characterization and compression of broadband laser pulses, circumventing disadvantages of common methods utilizing second or third harmonic light.

Acetone gas sensors based on graphene-ZnFe2O4 composite prepared by solvothermal method

In order to study the gas-sensing properties of graphene-ZnFe2O4 composite, graphene-mixed ZnFe2O4 with different mixing ratios are prepared via solvothermal method and characterized by X-ray diffraction using CuKα. Before preparing graphene-ZnFe2O4 composite, graphene is firstly prepared by reduction of graphene oxide with hydrazine hydrate and identified by FT-IR and Raman spectrometer. The gas-sensing experiments include the effects of graphene mixing weight and solvothermal temperature on the gas-sensing response, the selectivity and reproducibility, and the response of the sensor based on 0.125%G-ZnFe2O4 to acetone in various concentrations. The experimental results reveal that the mixing of graphene into ZnFe2O4 can lower the operating temperature of the sensors to acetone vapor, and the sensor based on 0.125%G-ZnFe2O4 (180°C, 10h) exhibits good selectivity and reproducibility to 10ppm acetone vapor at 275°C. So, the sensor based on 0.125%G-ZnFe2O4 (180°C, 10h) may be applied to detect diabetes mellitus via measuring the acetone vapor at low temperature if the selectivity and response are improved further and the amount relation of sensing response versus concentration of acetone is found.

Nonlinear optics of graphene in a strong magnetic field

Graphene placed in a magnetic field possesses an extremely high mid/far-infrared optical nonlinearity originating from its unusual band structure and selection rules for the optical transitions near the Dirac point. Here, we study the linear and nonlinear optical response of graphene in strong magnetic and optical fields using a quantum-mechanical density-matrix formalism. We calculate the power of the coherent terahertz radiation generated as a result of the four-wave mixing in graphene. We show that even one monolayer of graphene gives rise to an appreciable nonlinear frequency conversion efficiency and Raman gain for modest intensities of the incident infrared radiation.

Representative volume element to estimate buckling behavior of graphene/polymer nanocomposite

The aim of the research article is to develop a representative volume element using finite elements to study the buckling stability of graphene/polymer nanocomposites. Research work exploring the full potential of graphene as filler for nanocomposites is limited in part due to the complex processes associated with the mixing of graphene in polymer. To overcome some of these issues, a multiscale modeling technique has been proposed in this numerical work. Graphene was herein modeled in the atomistic scale, whereas the polymer deformation was analyzed as a continuum. Separate representative volume element models were developed for investigating buckling in neat polymer and graphene/polymer nanocomposites. Significant improvements in buckling strength were observed under applied compressive loading when compared with the buckling stability of neat polymer.

Room-temperature strong terahertz photon mixing in graphene

We demonstrate that single layer graphene exhibits a strong nonlinear photon-mixing effect in the terahertz frequency regime. Up to room temperature, the third-order nonlinear current in graphene grows rapidly with increasing temperature. The third-order nonlinear current can be as strong as the linear current under a moderate electric field strength of 104 V/cm. Because of the unique Dirac behavior of the graphene quasi-particles, low Fermi level and electron fillings optimizes the optical nonlinearity. Under a strong-field condition, the strong-field-induced Dirac fermion population redistribution and nonequilibrium carrier heating effects further amplify the optical nonlinearity of graphene. Our results suggest that doped graphene can potentially be utilized as a strong terahertz photon mixer in the room-temperature regime.

Full-band quantum-dynamical theory of saturation and four-wave mixing in graphene

The linear and nonlinear optical response of graphene are studied within a quantum-mechanical, full-band, steady-state density-matrix model. This nonpurtabative method predicts the saturatable absorption and saturable four-wave mixing of graphene. The model includes τ(1) and τ(2) time constants that denote carrier relaxation and quantum decoherence, respectively. Fits to existing experimental data yield τ(2) < 1 fs due to carrier-carrier scattering. τ(1) is found to be on the timescale from 250 fs to 550 fs, showing agreement with experimental data obtained by differential transmission measurements.

Influence of Landau-level mixing on Wigner crystallization in graphene

Graphene, with its massless linearly dispersing carriers, in the quantum Hall regime provides an instructive comparison to conventional two-dimensional systems in which carriers have a nonzero band mass and quadratic dispersion. We investigate the influence of Landau-level mixing in graphene on Wigner crystal states in the $n\text{th}$ Landau level obtained using single-Landau-level approximation. We show that the Landau-level mixing does not qualitatively change the phase diagram as a function of partial filling factor $\ensuremath{\nu}$ in the $n\text{th}$ level. We find that the inter-Landau-level mixing, which is quantified by relative occupations of the two Landau levels, ${\ensuremath{\rho}}_{n+1}/{\ensuremath{\rho}}_{n}$, oscillates around 2% and, in general, remains small $(l4%)$ irrespective of the Landau-level index $n$. Our results show that the single-Landau-level approximation is applicable in high Landau levels, even though the energy gap between the adjacent Landau levels vanishes.