arXiv subjects

A. L. Ivanov

Publications and source records attributed to A. L. Ivanov.

23 records · Page 2Linked to original sources

arXiv2003

Resonant acousto-optics of microcavity polaritons

We propose and analyze theoretically a resonant acousto-optic Stark effect for microcavity (MC) polaritons parametrically driven by a surface acoustic wave. For GaAs-based microcavities our scheme ``acoustic pumping - optical probing'' deals with surface acoustic waves of frequency $ν_{\rm SAW} \simeq 0.5 - 3$ GHz and intensity $I_{\rm SAW} \simeq 0.1 - 10$ mW/mm. The acoustically-induced stop gaps in the MC polariton spectrum drastically change the optical response of MC polaritons. Because an acoustically pumped intrinsic semiconductor microcavity remains in its ground electronic state, no many-body effects screen and weaken the resonant acousto-optic Stark effect. In the meantime, this allows us to work out an exactly-solvable model for resonant acousto-optics of MC polaritons which deals with giant acousto-optical nonlinearities. Finally, we discuss possible applications of the proposed resonant acoustic Stark effect for optical modulation and switching and describe an acousto-optic device based on a (GaAs) microcavity driven by a surface acoustic wave.

cond-mat.mes-hall↗

arXiv2002

Quantum diffusion of dipole-oriented indirect excitons in coupled quantum wells

A model for diffusion of statistically-degenerate excitons in (coupled) quantum wells is proposed and analysed. Within a microscopic approach, we derive a quantum diffusion equation, calculate and estimate the self-diffusion coefficient for excitons in quantum wells and derive a modified Einstein relation adapted to statistically-degenerated quasi-two-dimensional bosons. It is also shown that the dipole-dipole interaction of indirect excitons effectively screens long-range-correlated disorder in quantum wells. Numerical calculations are given for indirect excitons in GaAs/AlGaAs coupled quantum wells.

cond-mat.stat-mech↗

arXiv2001

Phonon-assisted relaxation kinetics of statistically-degenerate excitons in high-quality quantum wells

Acoustic-phonon-assisted thermalization kinetics of excitons in quantum wells (QWs) is developed for small concentrations of particles, $ρ_{\rm 2D} \lesssim 10^9$ cm$^{-1}$, when particle-particle interaction can be neglected while Bose-Einstein statistics already strongly influences the relaxation processes at low temperatures. In this case thermalization of QW excitons occurs through nonequilibrium states and is given by the following scenario. During the first transient stage, which lasts a few characteristic scattering times, the correlations with an initial distribution of QW excitons disappear. The next, adiabatic stage of thermalization usually takes many characteristic scattering times, depends only upon two control parameters, the lattice temperature $T_b$ and the degeneracy temperature $T_0 \propto ρ_{\rm 2D}$, and is characterized by a quasi-equilibrated distribution of high-energy QW excitons with effective temperature $T(t)$. We show that the thermalization law of high-energy particles is given by $δT(t) = T(t) - T_b \propto e^{-λ_0 t}/t$, where $λ_0$ is a marginal value of the continuous eigenvalue spectrum of the linearized kinetics. By analyzing the linearized phonon-assisted kinetics of statistically-degenerate QW excitons, we study the dependence $λ_0 =λ_0(T_b,T_0)$. Our numerical estimates refer to high quality GaAs and ZnSe QWs. Finally, we propose a special design of GaAs-based microcavities, which considerably weakens the bottleneck effect in relaxation of excitons (polaritons) and allows us to optimize the acoustic-phonon-assisted thermalization processes.

cond-mat↗

arXiv1999

Reply to ``Comment on `Inverse exciton series in the optical decay of an excitonic molecule' "

As a reply to the Comment by I.S. Gorban {\it et al.} (Phys. Rev. B, preceding paper) we summarize our criticism on their claim of the first observation of the $M$ series in $β$-ZnP$_2$. We support our analysis by reporting the first observation of inverse {\it polariton} series from the excitonic molecules selectively generated at ${\bf K}_m \simeq {\bf 0}$ in a CuCl single crystal. This observation and its explanation within the bipolariton model complete our proof of the biexcitonic origin of the inverse series.

cond-mat.str-el↗

arXiv1998

Bose-Einstein statistics in thermalization and photoluminescence of quantum well excitons

Quasi-equilibrium relaxational thermodynamics is developed to understand LA-phonon-assisted thermalization of Bose-Einstein distributed excitons in quantum wells. We study the quantum-statistical effects in the relaxational dynamics of the effective temperature of excitons $T = T(t)$. When $T$ is less than the degeneracy temperature $T_0$, well-developed Bose-Einstein statistics of quantum well excitons leads to nonexponential and density-dependent thermalization. At low bath temperatures $T_b \to 0$ the thermalization of quantum-statistically degenerate excitons effectively slows down and $T(t) \propto 1 / \ln t$. We also analyze the optical decay of Bose-Einstein distributed excitons in perfect quantum wells and show how nonclassical statistics influences the effective lifetime $τ_{opt}$. In particular, $τ_{opt}$ of a strongly degenerate gas of excitons is given by $2 τ_R$, where $τ_R$ is the intrinsic radiative lifetime of quasi-two-dimensional excitons. Kinetics of resonant photoluminescence of quantum well excitons during their thermalization is studied within the thermodynamic approach and taking into account Bose-Einstein statistics. We find density-dependent photoluminescence dynamics of statistically degenerate excitons. Numerical modeling of the thermalization and photoluminescence kinetics of quasi-two-dimensional excitons are given for GaAs/AlGaAs quantum wells.

cond-mat.stat-mech↗