arXiv subjects

S. V. Koniakhin

Publications and source records attributed to S. V. Koniakhin.

At least 19 recordsLinked to original sources

arXiv2025

Driven-dissipative turbulence in exciton-polariton quantum fluids

The present paper is devoted to comprehensive theoretical studies of exction-polariton quantum fluids specificities in the optics of their utilization for quantum turbulence research. We show that a non-trivial implementation of time-varying potential for excitation of quantum fluid (injection of quantized vortices) via the stirring procedure can be efficiently substituted with resonant excitation-based phase-imprinting techniques. The most efficient phase pattern corresponds to imprinting of tiles with randomly oriented plane waves in each. The resulting turbulent flows, spatial vortex distributions, and clustering statistics resemble those for the case of a conventional spoon-stirring scheme. We quantify the limitations on the lifetime and density depletion for the development and sustainability of quantum turbulence. The yield is the necessity to prevent the density depletion for more than one order of magnitude. Finally, we demonstrate that turbulence is robust with respect to alternating gain and loss at a certain range of modulation parameters, which corresponds to laser operating above and below condensation threshold.

cond-mat.mes-hall↗

arXiv2025

Phase locking of ring-shaped exciton-polariton condensates to coherent optical drive

The effect of an additional quasi-resonant drive on the dynamics of the ring-shaped incoherently pumped polariton condensates carrying angular momentum (vorticity) is studied theoretically. Numerical simulations of the 2D and 1D Gross-Pitaevskii equations show that the difference of the topological charges(vorticities) $Δn$ of the condensate and the quasi-resonant coherent drive plays a crucial role in the synchronization dynamics. It is shown that in an axially symmetric system, synchronization can only occur if $|Δn| = 0$, whereas in the other cases the phase of the condensate cannot be locked to the phase of the coherent drive. To explain this effect observed in the numerical simulations a perturbation theory is developed. The theory shows that the phase slip between the condensate and the coherent drive can be understood in terms of the motion of 2$π$ kinks. It is shown that the breaking of the axial symmetry can stop the motion of the kinks, allowing the phase locking of the condensate to the coherent drive.

cond-mat.mes-hall↗

arXiv2024

Skew scattering and ratchet effect in photonic graphene

The present paper is devoted to a comprehensive theoretical study of asymmetric (skew) scattering in photonic graphene, with the main focus on its realization with semiconductor microcavity exciton-polaritons. As an important consequence of the skew scattering, we prove the appearance of the ratchet effect in this system. Triangular defects in the form of missing micropillars in a regular honeycomb lattice are considered as ones that break the spatial inversion symmetry, thus providing the possibility of the ratchet effect. By means of the numerical solution of the effective Schrödinger equation, we provide microscopical insight into the process of skew scattering and determine indicatrices, cross-sections, and asymmetry parameters. In a system with multiple coherently oriented triangular defects, a macroscopic ratchet effect occurs as a unidirectional flux upon noise-like initial conditions. Our study broadens the concept of ratchet phenomena in the field of photonics and optics of exciton-polaritons.

cond-mat.mes-hall↗

arXiv2024

Optical Snake States in Photonic Graphene

We propose an optical analogue of electron snake states based on artificial gauge magnetic field in photonic graphene with effective strain implemented by varying distance between pillars. We develop an intuitive and exhaustive continuous model based on tight-binding approximation and compare it with numerical simulations of a realistic photonic structure. The allowed lateral propagation direction is shown to be strongly coupled to the valley degree of freedom and the proposed photonic structure may be used a valley filter.

cond-mat.mes-hall↗

arXiv2024

Raman peak shift and broadening in crystalline nanoparticles with lattice impurities

The effect of point-like lattice impurities on nanoparticle Raman spectra (RS) is studied using both numerical and analytical methods. Particular cases of replacement atoms of various masses, vacancies, and disorder in interatomic bonds are considered. It is shown that the disorder leads not only to the broadening of optical phonon lines but also to the shift of the corresponding Raman peak. The latter can be either positive (i.e., blueshift) or negative (redshift) depending on the type of impurities. Thus there is an additional contribution to the well-known redshift that occurs due to the size-quantization (confinement) effect. Considering nanometer-sized diamond particles as a representative example, we show that the broadening and the shift are, as a rule, of the same order of magnitude. The results are discussed in the framework of the self-consistent T-matrix approach. It is argued that both effects should be considered for accurate treatment of experimental Raman spectra. Simple recipes to do so are formulated for several important cases including NV centers in nanodiamonds.

cond-mat.mes-hall↗

arXiv2023

Localized and extended collective optical phonon modes in regular and random arrays of contacting nanoparticles: escape from phonon confinement

In the present paper, we utilize the coupled-oscillator model describing the hybridization of optical phonons in touching and/or overlapping particles in order to study the Raman spectra of nanoparticles organized into various types of regular and random arrays including nanosolids, porous media, and agglomerates with tightly bonded particles. For the nanocrystal solids, we demonstrate that the ratio of the size variance to the coupling strength allows us to judge the character (localized or propagating) of the optical phonon modes which left the particles of their origin and spread throughout an array. The relation between the shift and the broadening of the Raman peak and the coupling strength and the disorder is established for nanocrystal solids, agglomerates, and porous media providing us with information about the array structure, the structure of its constituents, and the properties of optical phonons.

cond-mat.mes-hall↗

arXiv2022

Simultaneous creation of multiple vortex-antivortex pairs in momentum space in photonic lattices

Engineering of the orbital angular momentum (OAM) of light due to interaction with photonic lattices reveals rich physics and motivates potential applications. We report the experimental creation of regularly-distributed quantized vortex arrays in momentum space by probing the honeycomb and hexagonal photonic lattices with a single focused Gaussian beam. For the honeycomb lattice, the vortices are associated with Dirac points and mimic the Berry curvature sources. However, we show that the resulting spatial patterns of vortices are strongly defined by the symmetry of the wave packet evolving in the optical lattice but not by lattice topological properties. Our findings reveal the underlying physics by connecting the symmetry and OAM conversion, and provide a simple and efficient method to create regularly-distributed multiple vortices by unstructured light.

physics.optics↗

arXiv2022

Coupled oscillators model for hybridized optical phonon modes in contacting nanosized particles and quantum dot molecules

Modification of optical phonon spectra in contacting nanoparticles as compared to the single ones is studied. Optical phonons in dielectric and semiconducting particles obey the Euclidean metric Klein-Fock-Gordon equation with Dirichlet boundary conditions. The latter is supposed to be solved numerically for manifolds of interpenetrating spheres. It is proposed to replace this problem with the simpler-to-solve coupled oscillators model (COM), where an oscillator is attributed to each phonon mode of a particle and the particles overlap leads to appearance of additional couplings for these oscillators with the magnitude proportional to the overlapped volume. For not too big overlaps this model describes solutions of the original eigenvalue problem on a good level of accuracy. In particular, it works beyond isotropic s modes, which has been demonstrated for p modes in dimer and also for tetramer. It is proposed to apply COM for the description of recently manufactured dimer nanoparticles and quantum dots. The obtained results are in agreement with the dynamical matrix method for optical phonons in nanodiamonds. The latter is used to demonstrate that the van der Waals contacts between faceted particles lead to very small modifications of the optical phonon spectra, which therefore could be neglected when discussing the propagation of vibrational excitations via a nanopowder. The possibility to distinguish between dimerized and size-distributed single particles from their Raman spectra is also considered.

cond-mat.mes-hall↗

arXiv2020

Topological turbulence in spin-orbit-coupled driven-dissipative quantum fluids of light generates high angular momentum states

We demonstrate the formation of a high angular momentum turbulent state in an exciton-polariton quantum fluid with TE-TM Spin-Orbit Coupling (SOC). The transfer of particles from quasi-resonantly cw pumped \spl component to \sm component is accompanied with the generation of a turbulent gas of quantum vortices by inhomogeneities. We show that this system is unstable with respect to the formation of bogolons at a finite wave vector, controlled by the laser detuning. In a finite-size cavity, the domains with this wave vector form a ring-like structure along the border of a cavity, with a gas of mostly same-sign vortices in the center. The total angular momentum is imposed by the sign of TE-TM SOC, the wave vector of instability, and the cavity size. This effect can be detected experimentally via local dispersion measurements or by interference. The proposed configuration thus allows simultaneous experimental studies of quantum turbulence and high-angular momentum states in continuously-pumped exciton-polariton condensates.

cond-mat.quant-gas↗

arXiv2019

Stationary quantum vortex street in a driven-dissipative quantum fluid of light

We investigate the formation of a new class of density-phase defects in a resonantly driven 2D quantum fluid of light. The system bistability allows the formation of low density regions containing density-phase singularities confined between high density regions. We show that in 1D channels, an odd (1-3) or even (2-4) number of dark solitons form parallel to the channel axis in order to accommodate the phase constraint induced by the pumps in the barriers. These soliton molecules are typically unstable and evolve toward stationary symmetric or anti-symmetric arrays of vortex streets straightforwardly observable in \emph{cw} experiments. The flexibility of this photonic platform allows implementing more complicated potentials such as maze-like channels, with the vortex streets connecting the entrances and thus solving the maze.

cond-mat.mes-hall↗

arXiv2019

Evidence of absorption dominating over scattering in light attenuation by nanodiamonds

We show an experimental evidence of the domination of absorption over scattering in absorbance spectra of detonation nanodiamonds. We perform the absorbance measurements on the UV-Vis spectrophotometer equipped with integrating sphere and compare them with conventional absorbance spectra. Additionally, we measure the scattering light intensity at the cuvette side wall (scattering at 90 degrees angle). The obtained experimental data were interpreted using the simulations of photon random walk in turbid media and Kubelka-Munk approach. The scattering cross sections and indicatrices were obtained by Mie theory. We discover that despite being very close to $λ^{-4}$ power law (like Rayleigh scattering) the light extinction by the primary 4 nm diamond crystallites is due to absorption only and scattering can be neglected. That is the reason why previously absorption and scattering contributions were confused. The scattering is governed only by the agglomerates of 100 nm and larger in size remaining in the hydrosols and their fraction can be effectively controlled by centrifugation. Only Mie theory reproduces correctly the close to $λ^{-2}$ scattering by the agglomerates accounting for the weird interplay between their size, fractal dimension, and dielectric properties. Finally, using the obtained absorbance spectra we estimate the fraction of non diamond phase in nanodiamonds and their agglomerates.

cond-mat.mes-hall↗

arXiv2019

2D Quantum Turbulence in Polariton Condensates

The coexistence of the energy and enstrophy cascades in 2D quantum turbulence is one of the important open questions in the studies of quantum fluids. Here, we show that polariton condensates are particularly suitable for the possible observation of scaling on sufficiently large scales. The shape of raw energy spectra depends on the procedure of condensate excitation (stirring), but the energy spectra of clustered vortices always exhibit the -5/3 power law. In the optimal case, the cascade can be observed over almost 2 decades.

cond-mat.mes-hall↗

arXiv2018

Analog Kerr Black hole and Penrose effect in a Bose-Einstein Condensate

Analog physics allows simulating inaccessible objects, such as black holes, in the lab. We propose to implement an acoustic Kerr black hole with quantized angular momentum in a polariton Bose-Einstein condensate. We show that the metric of the condensate is equivalent to the Kerr's one, exhibiting a horizon and an ergosphere. Using topological defects as test particles, we demonstrate an analog Penrose effect, extracting the rotation energy of the black hole. The particle trajectories are well described by the time-like geodesics of the Kerr metric, confirming the potential of analog gravity.

cond-mat.quant-gas↗

arXiv2018

Raman spectra of nanoparticles: elasticity theory-like approach for optical phonons

A simple way to investigate theoretically the Raman spectra (RS) of nonpolar nanoparticles is proposed. For this aim we substitute the original lattice optical phonon eigenproblem by the continuous Klein-Fock-Gordon-like equation with Dirichlet boundary conditions. This approach provides the basis for the continuous description of optical phonons in the same manner how the elasticity theory describes the longwavelength acoustic phonons. Together with continuous reformulation of the bond polarization model it allows to calculate the RS of nanoparticles without referring to their atomistic structure. It ensures the powerful tool for interpreting the experimental data, studying the effects of particle shape and their size distribution. We successfully fit recent experimental data on very small diamond and silicon particles, for which the commonly used phonon confinement model fails. The predictions of our theory are compared with recent results obtained within the dynamical matrix method - bond polarization model (DMM-BPM) approach and an excellent agreement between them is found. The advantages of the present theory are its simplicity and the rapidity of calculations. We analyze how the RS are affected by the nanoparticle faceting and propose a simple power law for Raman peak position dependence on the facets number. The method of powder RS calculations is formulated and the limitations on the accuracy of our analysis are discussed.

cond-mat.mes-hall↗

arXiv2018

Novel approach to Raman spectra of nanoparticles

In crystalline nanoparticles the Raman peak is downshifted with respect to the bulk material and has asymmetric broadening. These effects are straightly related to the finite size of nanoparticles, giving the perspective to use the Raman spectroscopy as the size probe. By combining the dynamical matrix method (DMM) and the bond polarization model (BPM), we develop a new (DMM-BPM) approach to the description of Raman spectra for random arrays of nanoparticles. The numerical variant of this approach is suitable for the description of small particles, whereas its simplier to implement analytical version allows to obtain the Raman spectra of arbitrary sized particles. Focusing on nanodiamond powders, the DMM-BPM theory is shown to fit the most recent experimental data much better than the commonly used phonon confinement model (PCM), especially for small enough nanoparticles.

cond-mat.mes-hall↗

arXiv2017

Ultracentrifugation for ultrafine nanodiamond fractionation

In this paper we propose a method for ultrafine fractionation of nanodiamonds using the differential centrifugation in the fields up to 215000g. The developed protocols yield 4-6 nm fraction giving main contribution to the light scattering intensity. The desired 4-6 nm fraction can be obtained from various types of initial nanodiamonds: three types of detonation nanodiamonds differing in purifying methods, laser synthesis nanodiamonds and nanodiamonds made by milling. The characterization of the obtained hydrosols was conducted with Dynamic Light Scattering, Zeta potential measurements, powder XRD and TEM. According to powder XRD and TEM data ultracentrifugation also leads to a further fractionation of the primary diamond nanocrystallites in the hydrosols from 4 to 2 nm.

physics.app-ph↗

arXiv2016

Molecular dynamics-based refinement of nanodiamond size measurements obtained with dynamic light scattering

The determination of particle size by dynamic light scattering uses the Stokes-Einstein relation, which can break down for nanoscale objects. Here we employ a molecular dynamics simulation of fully solvated 1-5 nm carbon nanoparticles for the refinement of the experimental data obtained for nanodiamonds in water by using dynamic light scattering. We performed molecular dynamics simulations in differently sized boxes and calculated nanoparticles diffusion coefficients using the velocity autocorrelation function and mean-square displacement. We found that the predictions of the Stokes-Einstein relation are accurate for nanoparticles larger than 3 nm while for smaller nanoparticles the diffusion coefficient should be corrected and different boundary conditions should be taken into account.

physics.flu-dyn↗

arXiv2016

Drag of electrons in graphene by substrate surface polar phonons

It is known that electron scattering by surface polar phonons (SPPs) of the substrate reduces their mobility in supported graphene. However, there is no experimental evidence for contribution of drag of electrons by SPP to thermoelectric phenomena in graphene: graphene thermopower exhibits good agreement with Mott's law, which means that the diffusion contribution to the thermopower is dominant in a wide range of carrier densities and temperatures. Here we develop a complete theory of drag of electrons in graphene by SPP. By solving Boltzmann transport equation for electrons scattered by SPPs we derive SPP drag contribution to the thermopower in graphene. Compared to diffusion thermopower, obtained values appear to be one order of magnitude lower for various substrates. This can be explained by low occupation number of the SPPs and short mean free path of such phonons stemming from their small group velocity. We conclude that experiments on thermopower in graphene can be treated within the framework of Mott's law.

cond-mat.mes-hall↗