Hyperspherical theory of anisotropic exciton

A new approach to the theory of anisotropic exciton based on Fock transformation, i.e., on a stereographic projection of the momentum to the unit 4-dimensional (4D) sphere, is developed. Hyperspherical functions are used as a basis of the perturbation theory. The binding energies, wave functions and oscillator strengths of elongated as well as flattened excitons are obtained numerically. It is shown that with an increase of the anisotropy degree the oscillator strengths are markedly redistributed between optically active and formerly inactive states, making the latter optically active. An approximate analytical solution of the anisotropic exciton problem taking into account the angular momentum conserving terms is obtained. This solution gives the binding energies of moderately anisotropic exciton with a good accuracy and provides a useful qualitative description of the energy level evolution.Comment: 23 pages, 8 figure

Bistability and nonequilibrium transitions in the optically polarized system of cavity polaritons under nanosecond-long resonant excitation

The polarization dependence of nonequilibrium transitions in a multistable cavity-polariton system is studied under a nanosecond long resonant optical excitation at the normal and magic angle incidences with various polarizations of the pump beam. The temporal correlations between the frequency, intensity, and optical polarization of the intra-cavity field, which all undergo sharp threshold-like changes due to the spin dependent interaction of cavity polaritons, are visualized. The observed dynamics cannot be reproduced within the conventional semi-classical model based on the Gross-Pitaevskii equations. To explain the observed phenomena, it is necessary to take into account the unpolarized exciton reservoir which brings on additional blueshift of bright excitons, equal in the $\sigma^+$ and $\sigma^-$ polarization components. This model explains the effect of polarization instability under both pulsed and continuous wave resonant excitation conditions, consistently with the spin ring pattern formation that has recently been observed under Gaussian shaped excitation.Comment: 13 pages, 13 figure

Bose-Einstein Condensation of Excitons: Reply to Tikhodeev's Criticism

The extended version of our reply to Comment on ``Critical Velocities in Exciton Superfluidity'' by S. G. Tikhodeev (Phys. Rev. Lett., 84 (2000), 3502 or from http://prl.aps.org/) is presented here. The principal question is discussed: does the moving exciton-phonon packet contain the coherent `nucleus', or the exciton-phonon condensate?Comment: 3 pages in LaTe

Relation between inelastic electron tunneling and vibrational excitation of single adsorbates on metal surfaces

We analyse theoretically a relation between the vibrational generation rate of a single adsorbate by tunneling electrons and the inelastic tunneling (IET) current in scanning tunneling microscope, and the influence of the vibrational excitations on the rate of adsorbate motions. Special attention is paid to the effects of finite lifetime of the vibrational excitations. We show that in the vicinity and below the IET threshold the rate of adsorbate motion deviates from a simple power-law dependence on the bias voltage due to the effects of bath temperature and adsorbate vibrational lifetime broadenings. The temperature broadening appears to be confined near the threshold voltage within a narrow region of several $k_B T$, whereas the lifetime broadening manifests itself in a much wider region of applied voltages below the IET threshold.Comment: 8 pages including 4 figure

Controlling circular polarization of light emitted by quantum dots using chiral photonic crystal slab

We study the polarization properties of light emitted by quantum dots that are embedded in chiral photonic crystal structures made of achiral planar GaAs waveguides. A modification of the electromagnetic mode structure due to the chiral grating fabricated by partial etching of the wave\-guide layer has been shown to result in a high circular polarization degree $\rho_c$ of the quantum dot emission in the absence of external magnetic field. The physical nature of the phenomenon can be understood in terms of the reciprocity principle taking into account the structural symmetry. At the resonance wavelength, the magnitude of $|\rho_c|$ is predicted to exceed 98%. The experimentally achieved value of $|\rho_c|=81$% is smaller, which is due to the contribution of unpolarized light scattered by grating defects, thus breaking its periodicity. The achieved polarization degree estimated removing the unpolarized nonresonant background from the emission spectra can be estimated to be as high as 96%, close to the theoretical prediction

Nonlinear dynamics of polariton scattering in semiconductor microcavity: bistability vs stimulated scattering

We demonstrate experimentally an unusual behavior of the parametric polariton scattering in semiconductor microcavity under a strong cw resonant excitation. The maximum of the scattered signal above the threshold of stimulated parametric scattering does not shift along the microcavity lower polariton branch with the change of pump detuning or angle of incidence but is stuck around the normal direction. We show theoretically that such a behavior can be modelled numerically by a system of Maxwell and nonlinear Schroedinger equations for cavity polaritons and explained via the competition between the bistability of a driven nonlinear MC polariton and the instabilities of parametric polariton-polariton scattering.Comment: 5 pages, 4 Postscript figures; corrected typo

Analytical normalization of resonant states in photonic crystal slabs and periodic arrays of nanoantennas at oblique incidence

We present an analytical formulation for the normalization of resonant states at oblique incidence in one- and two-dimensional periodic structures with top and bottom boundaries to homogeneous space, such as photonic crystal slabs and arrays of nanoantennas. The normalization is validated by comparing the resonant state expansion using one and two resonant states with numerically exact results. The predicted changes of resonance frequency and linewidth due to perturbations of refractive index or geometry can be used to study resonantly enhanced refractive index sensing as well as the influence of disorder. In addition, the normalization is essential for the calculation of the Purcell factor

Optical properties of photonic crystal slabs with asymmetrical unit cell

Using the unitarity and reciprocity properties of the scattering matrix, we analyse the symmetry and resonant optical properties of the photonic crystal slabs (PCS) with complicated unit cell. We show that the reflectivity is not changed upon the 180deg-rotation of the sample around the normal axis, even in PCS with asymmetrical unit cell. Whereas the transmissivity becomes asymmetrical if the diffraction or absorption are present. The PCS reflectivity peaks to unity near the quasiguided mode resonance for normal light incidence in the absence of diffraction, depolarisation, and absorptive losses. For the oblique incidence the full reflectivity is reached only in symmetrical PCS.Comment: 5 pages, 2 Postscript figure

Circularly polarized lasing in chiral modulated semiconductor microcavity with GaAs quantum wells

This work has been funded by Russian Scientific Foundation (Grant No. 14-12-01372) and State of Bavaria.We report close to circularly polarized lasing at ћω = 1.473 and 1.522 eV from an AlAs/AlGaAs Bragg microcavity, with 12 GaAs quantum wells in the active region and chirally etched upper distributed Bragg refractor under optical pump at room temperature. The advantage of using the chiral photonic crystal with a large contrast of dielectric permittivities is its giant optical activity, allowing to fabricate a very thin half-wave plate, with a thickness of the order of the emitted light wavelength, and to realize the monolithic control of circular polarization.PostprintPeer reviewe