arXiv subjects

A. N. Poddubny

Publications and source records attributed to A. N. Poddubny.

At least 37 records · Page 2Linked to original sources

arXiv2014

Strong Purcell effect in anisotropic $\varepsilon$-near-zero metamaterials

We theoretically demonstrate the strong Purcell effect in $\varepsilon$-near-zero ultra-anisotropic uniaxial metamaterials with elliptic isofrequency surface. Contrary to the hyperbolic metamaterials, the effect does not rely on the diverging density of states and evanescent waves. As a result, both the radiative decay rate and the far-field emission power are enhanced. The effect can be realized in the periodic layered metal-dielectric nanostructures with complex unit cell containing two different metallic layers.

physics.optics↗

arXiv2014

Direct bandgap silicon quantum dots achieved via electronegative capping

We propose a novel concept of achieving silicon quantum dots with radiative rates enhanced by more than two orders of magnitude up to the values characteristic for direct band gap semiconductors. Our tight-binding simulations show how the surface engineering can dramatically change the density of confined electrons in real- and $k$-space and give rise to the new conduction band levels in $Γ$-valley, thus promoting the direct radiative transitions. The effect may be realized by covering the silicon dots with covalently bonded electronegative ligands, such as alkyl or teflon chains and/or by embedding in highly electronegative medium.

cond-mat.mes-hall↗

arXiv2014

Resonant Brillouin scattering of excitonic polaritons in multiple-quantum-well structures

We present theoretical and experimental study of resonant Brillouin scattering of excitonic polaritons in one-dimensional multiple-quantum-well structure. We obtain general analytical results for the scattering light spectra, valid for arbitrary quantum well arrangement. Application of our theory to the specific case of short-period superlattice shows a perfect quantitative agreement with experimental results for the height, width and position of the Brillouin scattering peaks and allows us to determine the energy, radiative and nonradiative decay rates of quantum well excitons. We reveal the signatures of excitonic polariton formation in the scattering spectra and show, that the spectral width and height are strongly sensitive to the number of wells in the sample.

cond-mat.mes-hall↗

arXiv2013

Radiative topological states in resonant photonic crystals

We present a theory of topological edge states in one-dimensional resonant photonic crystals with a compound unit cell. Contrary to the traditional electronic topological states the states under consideration are radiative, i.e., they decay in time due to the light escape through the structure boundaries. We demonstrate that the states survive despite their radiative decay and can be detected both in time- and frequency-dependent light reflection.

cond-mat.mes-hall↗

arXiv2013

Time-resolved second-order correlations of microcavity photons

The time dependence of the correlations between the photons, emitted from the microcavity with embedded quantum dot under incoherent pumping, is studied theoretically. Analytical expressions for the second-order correlation function g2(t) are presented in strong and weak coupling regimes. At moderate pumping the correlation function demonstrates Rabi oscillations, while at larger pumping it shows monoexponential decay. The decay time of the correlations nonmonotonously depends on the pumping value and has a maximum corresponding to the self-quenching transition.

cond-mat.mes-hall↗

arXiv2013

Phonon decay in silicon nanocrystals

The decay of the optical phonon into the two phonons of smaller energy is calculated for Si nanocrystals. The rate of the process is in the range of 1 to 10 ps. Such anharmonic phonon decay may control the energy relaxation rate of excited carriers in Si/SiO$_2$ nanocrystals. Relevance of the phonon decay to the experimentally observed hot carrier photoluminescence is discussed.

cond-mat.mtrl-sci↗

arXiv2012

Collective effects in emission of quantum dots strongly coupled to a microcavity photon

A theory of non-linear emission of quantum dot ensembles coupled to the optical mode of the microcavity is presented. Numerical results are compared with analytical approaches. The effects of exciton-exciton interaction within the quantum dots and with the reservoir formed by nonresonant pumping are considered. It is demonstrated, that the nonlinearity due to the interaction strongly affects the shape of the emission spectra. The collective superradiant mode of the excitons is shown to be stable against the non-linear effects.

cond-mat.mes-hall↗

arXiv2012

Reflection of short polarized optical pulses from periodic and aperiodic multiple quantum well structures

We study the reflection of polarized optical pulses from resonant photonic structures formed by periodic, Fibonacci, and gradient sequences of quantum wells. The form and polarization of the reflected pulse are shown to be determined by the structure design and optical length. In structures with periodic quantum well arrangement, the response to ultrashort pulse is an optical signal with a sharp rise followed by an exponential decay or Bessel beats depending on the structure length. The duration of reflected pulses non-monotonically depends on the number of quantum wells reaching the minimum for a certain structure length which corresponds to the transition from superradiant to photonic-crystalline regime. We also study the conversion of pulse polarization in the longitudinal external magnetic field which splits the exciton resonance. Comparing periodic, Fibonacci, and gradient structures we show that the latter are more efficient for the conversion from linear to circular polarization.

cond-mat.mes-hall↗

arXiv2011

Anomalous Suppression of Valley Splittings in Lead Salt Nanocrystals without Inversion Center

Atomistic sp3d5s* tight-binding theory of PbSe and PbS nanocrystals is developed. It is demonstrated, that the valley splittings of confined electrons and holes strongly and peculiarly depend on the geometry of a nanocrystal. When the nanocrystal lacks a microscopic center of inversion and has T_d symmetry, the splitting is strongly suppressed as compared to the more symmetric nanocrystals with O_h symmetry, having an inversion center.

cond-mat.mes-hall↗

arXiv2011

Purcell effect in small metallic cavities

We have studied theoretically the Purcell factor which characterizes a change in the emission rate of an electric or magnetic dipole embedded in the center of a spherical cavity. The main attention is paid to the analysis of cavities with radii small compared to the wavelength. It is shown that the Purcell factor in small metallic cavities varies in a wide range depending on the ratio of the cavity size to the skin depth.

cond-mat.mes-hall↗

arXiv2010

Optical transitions and energy relaxation of hot carriers in Si nanocrystals

Dynamics of hot carriers confined in Si nanocrystals is studied theoretically using atomistic tight binding approach. Radiative, Auger-like and phonon-assisted processes are considered. The Auger-like energy exchange between electrons and holes is found to be the fastest process in the system. However the energy relaxation of hot electron-hole pair is governed by the single optical phonon emission. For a considerable number of states in small nanocrystals single-phonon processes are ruled out by energy conservation law.

cond-mat.mes-hall↗

arXiv2010

Wood anomalies in resonant photonic quasicrystals

A theory of light diffraction from planar quasicrystalline lattice with resonant scatterers is presented. Rich structure, absent in the periodic case, is found in specular reflection spectra, and interpreted as a specific kind of Wood anomalies, characteristic for quasicrystals. The theory is applied to semiconductor quantum dots arranged in Penrose tiling.

cond-mat.mes-hall↗

arXiv2010

Non-linear emission spectra of quantum dots strongly coupled to photonic mode

A theory of optical emission of quantum dot arrays in quantum microcavities is developed. The regime of the strong coupling between the quantum dots and photonic mode of the cavity is considered. The quantum dots are modeled as two-level systems. In the low pumping (linear) regime the emission spectra are mainly determined by the superradiant mode where the effective dipoles of the dots oscillate in phase. In the non-linear regime the superradiant mode is destroyed and the emission spectra are sensitive to the parity of quantum dot number. Further increase of the pumping results in the line width narrowing being an evidence of the lasing regime.

cond-mat.mes-hall↗

arXiv2009

Resonant Photonic Quasicrystalline and Aperiodic Structures

We have theoretically studied propagation of exciton-polaritons in deterministic aperiodic multiple-quantum-well structures, particularly, in the Fibonacci and Thue-Morse chains. The attention is concentrated on the structures tuned to the resonant Bragg condition with two-dimensional quantum-well exciton. The superradiant or photonic-quasicrystal regimes are realized in these structures depending on the number of the wells. The developed theory based on the two-wave approximation allows one to describe analytically the exact transfer-matrix computations for transmittance and reflectance spectra in the whole frequency range except for a narrow region near the exciton resonance. In this region the optical spectra and the exciton-polariton dispersion demonstrate scaling invariance and self-similarity which can be interpreted in terms of the ``band-edge'' cycle of the trace map, in the case of Fibonacci structures, and in terms of zero reflection frequencies, in the case of Thue-Morse structures.

cond-mat.mes-hall↗

arXiv2008

Collective modes of quantum dot ensembles in microcavities

Emission spectra of quantum dot arrays in zero-dimensional microcavities are studied theoretically, and it is shown that they are determined by the competition between the formation of the collective superradiant mode and inhomogeneous broadening. The random sources method for the calculation of photoluminescence spectra under a non-resonant pumping is developed, and a microscopic justification of the random sources method within a framework of the standard diagram technique is given. The emission spectra of a microcavity are analyzed with allowance for the spread of exciton states energies caused by an inhomogeneous distribution of quantum dots and a tunneling between them. It is demonstrated that in the case of a strong tunneling coupling the luminescence spectra are sensitive to the geometric positions of the dots, and the collective mode can, under certain conditions, be stabilized by the random tunnel junctions.

cond-mat.mes-hall↗

arXiv2008

Electron-phonon Interaction in Non-polar Quantum Dots Induced by the Amorphous Polar Environment

We propose a mechanism of energy relaxation for carriers confined in a non-polar quantum dot surrounded by an amorphous polar environment. The carrier transitions are due to their interaction with the oscillating electric field induced by the local vibrations in the surrounding amorphous medium. We demonstrate that this mechanism controls energy relaxation for electrons in Si nanocrystals embedded in a SiO$_2$ matrix, where conventional mechanisms of electron-phonon interaction are not efficient.

cond-mat.mes-hall↗

arXiv2008

Carrier relaxation in Si/SiO$_2$ quantum dots

Carrier relaxation due to both optical and nonradiative intraband transitions in silicon quantum dots in SiO$_2$ has been considered. Interaction of confined holes with optical phonons has been studied. The Huang-Rhys factor is calculated for such transitions. The probability of intraband transition of a confined hole emitting several optical phonons is estimated.

cond-mat.mtrl-sci↗

arXiv2007

Resonant Fibonacci Quantum Well Structures

We propose a resonant one-dimensional quasicrystal, namely, a multiple quantum well (MQW) structure satisfying the Fibonacci-chain rule with the golden ratio between the long and short inter-well distances. The resonant Bragg condition is generalized from the periodic to Fibonacci MQWs. A dispersion equation for exciton-polaritons is derived in the two-wave approximation, the effective allowed and forbidden bands are found. The reflection spectra from the proposed structures are calculated as a function of the well number and detuning from the Bragg condition.

cond-mat.mes-hall↗