arXiv subjects

Vitaliy N. Pustovit

Publications and source records attributed to Vitaliy N. Pustovit.

12 recordsLinked to original sources

arXiv2018

Saddle point singularity and optical phase transition in bilayer hyperbolic metamaterials

We study theoretically and numerically high density of states for hyperbolic bilayered metamaterials (HMM). It reveals that density response of HMM is reminiscent of Fermi electronic band structure of metal or semiconductors. By the method of Green function a van Hove type singularity is found in photonic density spectra of HMM with saddle point localization on photonic Fermi surface (FS) of metamaterial. Similar to the electronic systems, the photonic FS experiences instabilities induced by the changes in volume fractions of its constituents that leads to the Lifshitz type zero-temperature phase transition between FS of types I and II hyperbolic states at the topology protected critical point.

physics.app-ph↗

arXiv2016

Surface plasmon amplification by stimulated emission of radiation in hyperbolic metamaterials

We study theoretically and numerically spasing conditions and optical dynamics of a composite hyperbolic metamaterial interacting with gain molecules. By combining Maxwell-Bloch equations with Green's function approach, we calculate lasing frequency and threshold population inversion for various gain density in the gain layer. We demonstrate high level of enhancement for photonic density of states in spacious spectral range provided by hyperbolic metastructures. We find that direct dipole-dipole interactions between molecules in the gain layer has a negligible effect on spasing conditions. We identify a region of parameters in which spasing can occur considering these effects.

cond-mat.mes-hall↗

arXiv2016

Coulomb and quenching effects in small nanoparticle-based spasers

We study numerically the effect of mode mixing and direct dipole-dipole interactions between gain molecules on spasing in a small composite nanoparticles with a metallic core and a dye-doped dielectric shell. By combining Maxwell-Bloch equations with Green's function formalism, we calculate lasing frequency and threshold population inversion for various gain densities in the shell. We find that gain coupling to nonresonant plasmon modes has a negligible effect on spasing threshold. In contrast, the direct dipole-dipole coupling, by causing random shifts of gain molecules' excitation frequencies, hinders reaching the spasing threshold in small systems. We identify a region of parameter space in which spasing can occur considering these effects.

cond-mat.mes-hall↗

arXiv2013

Cooperative amplification of energy transfer in plasmonic systems

We study cooperative effects in energy transfer (ET) from an ensemble of donors to an acceptor near a plasmonic nanostructure. We demonstrate that in cooperative regime ET takes place from plasmonic superradiant and subradiant states rather than from individual donors leading to a significant increase of ET efficiency. The cooperative amplification of ET relies on the large coupling of superradiant states to external fields and on the slow decay rate of subradiant states. We show that superradiant and subradiant ET mechanisms are efficient in different energy domains and therefore can be utilized independently. We present numerical results demonstrating the amplification effect for a layer of donors and an acceptor on a spherical plasmonic nanoparticle.

cond-mat.mes-hall↗

arXiv2012

Fluorescence quenching near small metal nanoparticles

We develop a microscopic model for fluorescence of a molecule (or semiconductor quantum dot) near a small metal nanoparticle. When a molecule is situated close to metal surface, its fluorescence is quenched due to energy transfer to the metal. We perform quantum-mechanical calculations of energy transfer rates for nanometer-sized Au nanoparticles and find that non-local and quantum-size effects significantly enhance dissipation in metal as compared to those predicted by semiclassical electromagnetic models. However, the dependence of transfer rates on molecule's distance to metal nanoparticle surface, $d$, is significantly weaker than the $d^{-4}$ behavior for flat metal surface with a sharp boundary predicted by previous calculations within random phase approximation.

cond-mat.mes-hall↗

arXiv2011

Resonance energy transfer near metal nanostructures mediated by surface plasmons

We develop a unified theory of plasmon-assisted resonance energy transfer (RET) between molecules near a metal nanostructure that maintains energy balance between transfer, dissipation, and radiation. We show that in a wide range of parameters, including in the near field, RET is dominated by plasmon-enhanced radiative transfer (PERT) rather than by a nonradiative transfer mechanism. Our numerical calculations performed for molecules near the Ag nanoparticle indicate that RET magnitude is highly sensitive to molecules' positions.

cond-mat.mes-hall↗

arXiv2010

Plasmon-mediated superradiance near metal nanostructures

We develop a theory of cooperative emission of light by an ensemble of emitters, such as fluorescing molecules or semiconductor quantum dots, located near a metal nanostructure supporting surface plasmon. The primary mechanism of cooperative emission in such systems is resonant energy transfer between emitters and plasmons rather than the Dicke radiative coupling between emitters. We identify two types of plasmonic coupling between the emitters, (i) plasmon-enhanced radiative coupling and (ii) plasmon-assisted nonradiative energy transfer, the competition between them governing the structure of system eigenstates. Specifically, when emitters are removed by more than several nm from the metal surface, the emission is dominated by three superradiant states with the same quantum yield as a single emitter, resulting in a drastic reduction of ensemble radiated energy, while at smaller distances cooperative behavior is destroyed by nonradiative transitions. The crossover between two regimes can be observed in distance dependence of ensemble quantum efficiency. Our numerical calculations incorporating direct and plasmon-assisted interactions between the emitters indicate that they do not destroy the plasmonic Dicke effect.

cond-mat.mes-hall↗

arXiv2009

Size-dependent effects in solutions of small metal nanoparticles

A new theoretical approach for the calculation of optical properties of complex solutions is proposed. It is based on a dielectric matrix with included small metallic inclusions (less than 3 nm) of spherical shape. We take into account the mutual interactions between the inclusions and the quantum finite-size effects. On the basis of the effective medium model, TDLDA and Kohn-Sham theories, some analytical expressions for the effective dielectric permittivity of the solution are obtained.

cond-mat.soft↗

arXiv2008

Cooperative emission of light by an ensemble of dipoles near a metal nanostucture: The plasmonic Dicke effect

We identify a new mechanism for cooperative emission of light by an ensemble of N dipoles near a metal nanostructure supporting a surface plasmon.The cross-talk between emitters due to virtual plasmon exchange leads to a formation of three plasmonic super-radiant modes whose radiative decay rates scales with N, while the total radiated energy is thrice that of a single emitter. Our numerical simulations indicate that the plasmonic Dicke effect survives non-radiative losses in the metal.

cond-mat.mtrl-sci↗

arXiv2008

Bounds for effective dielectric permittivity in differential medium approximation

Theoretical approach is proposed to description of dielectric properties of matrix disperse systems which consists of dielectric matrix with embedded in metallic inclusions. On the basis of effective differential medium approximation the analytical expressions are obtained for the effective dielectric permittivity of the matrix disperse system with inclusions of spherical and ellipsoidal shape. The analysis of limits of possible values of the real and imaginary parts of is carried out depending on system parameters.

cond-mat.soft↗

arXiv2006

Microscopic theory of surface-enhanced Raman scattering in noble-metal nanoparticles

We present a microscopic model for surface-enhanced Raman scattering (SERS) from molecules adsorbed on small noble-metal nanoparticles. In the absence of direct overlap of molecular orbitals and electronic states in the metal, the main enhancement source is the strong electric field of the surface plasmon resonance in a nanoparticle acting on a molecule near the surface. In small particles, the electromagnetic enhancement is strongly modified by quantum-size effects. We show that, in nanometer-sized particles, SERS magnitude is determined by a competition between several quantum-size effects such as the Landau damping of surface plasmon resonance and reduced screening near the nanoparticle surface. Using time-dependent local density approximation, we calculate spatial distribution of local fields near the surface and enhancement factor for different nanoparticles sizes.

cond-mat.mes-hall↗

arXiv2004

Finite-Size Effects in Surface-Enhanced Raman Scattering from Molecules Adsorbed on Noble-Metal Nanoparticles

We study the role of strong electron confinement in surface-enhanced Raman scattering from molecules adsorbed on small noble-metal particles. We describe a new source of Raman signal enhancement which originates from different behavior of sp-band and d-band electron densities near the particle boundary. In small particles, a spillover of sp-electron wave-functions beyond the classical radius gives rise to a thin layer with diminished population of d-electrons. In this surface layer, the screening of sp-electrons by d-band electron background is reduced. We demonstrate that the interplay between finite-size and underscreening effects results in an increase of the surface plasmon local field acting on a molecule located in a close proximity to the particle boundary. Our calculations, based on two-region model, show that the additional enhancement of Raman signal gets stronger for smaller nanoparticles due to a larger volume fraction of underscreened region.

cond-mat.mes-hall↗