arXiv subjects

I. A. Shelykh

Publications and source records attributed to I. A. Shelykh.

At least 127 records · Page 7Linked to original sources

arXiv2015

Optical control of spin textures in quasi-one-dimensional polariton condensates

We investigate, through polarization-resolved spectroscopy, the spin transport by propagating polariton condensates in a quasi one-dimensional microcavity ridge along macroscopic distances. Under circularly polarized, continuous-wave, non-resonant excitation, a sinusoidal precession of the spin in real space is observed, whose phase depends on the emission energy. The experiments are compared with simulations of the spinor-polariton condensate dynamics based on a generalized Gross-Pitaevskii equation, modified to account for incoherent pumping, decay and energy relaxation within the condensate.

cond-mat.mes-hall↗

arXiv2015

Lamb Shift of Energy Levels in Quantum Rings

We study the vacuum radiative corrections to energy levels of a confined electron in quantum rings. The calculations are provided for the Lamb shift of energy levels in low-momentum region of virtual photons and for both one-dimensional and two-dimensional quantum rings. We show that contrary to the well known case of a hydrogen atom the value of the Lamb shift increases with the magnetic momentum quantum number m. We also investigate the dependence of the Lamb shift on magnetic flux piercing the ring and demonstrate a presence of magnetic-flux-dependent oscillations. For one-dimensional ring the value of the shift strongly depends on the radius of the ring. It is extremely small for semiconductor rings but can attain measurable quantities in natural organic ring-shape molecules, such as benzene, cycloalcanes and porphyrins.

quant-ph↗

arXiv2014

Exciton-photon correlations in bosonic condensates of exciton-polaritons

Exciton-polaritons are mixed light-matter quasiparticles. We have developed a statistical model describing stochastic exciton-photon transitions within a condensate of exciton polaritons. We show that the exciton-photon correlator depends on the "hidden variable" which characterizes the rate of exciton-photon transformations in the condensate. We discuss implications of this effect for the quantum statistics of photons emitted by polariton lasers.

cond-mat.mes-hall↗

arXiv2014

Spanning the full Poincaré sphere with polariton Rabi oscillations

We propose theoretically and demonstrate experimentally a generation of light pulses whose polarization varies temporally to cover selected areas of the Poincaré sphere with tunable swirling speed and total duration (1 ps and 10 ps respectively in our implementation). The effect relies on the Rabi oscillations of two polarized fields in the strong coupling regime, excited by two counter-polarized and delayed pulses. The interferences of the oscillating fields result in the precession of the Stokes vector of the emitted light while polariton lifetime imbalance results in its drift from a circle on the sphere of controllable radius to a single point at long times. The positioning of the initial and final states allows to engineer the type of polarization spanning, including a full sweeping of the Poincaré sphere. The universality and simplicity of the scheme should allow for the deployment of time varying polarization fields at a technologically exploitable level.

cond-mat.quant-gas↗

arXiv2014

Spatial Coherence Properties of One-Dimensional Exciton-Polariton-Condensates

In this work, we combine a systematic experimental investigation of the power- and temperaturedependent evolution of the spatial coherence function, g(1) (r), in a one-dimensional excitonpolariton channel with a modern microscopic numerical theory based on a stochastic master equation approach. The spatial coherence function g(1) (r) is extracted via high-precision Michelson interferometry, which allows us to demonstrate that in the regime of non-resonant excitation, the dependence g(1) (r) reaches a saturation value with a plateau, determined by the intensity of pump and effective temperature of the crystal lattice. The theory, which was extended to allow for treating incoherent excitation in a stochastic frame, matches the experimental data with good qualitative and quantitative agreement. This allows us to verify the prediction that the decay of the off-diagonal long range order can be almost fully suppressed in one-dimensional condensate systems.

cond-mat.mes-hall↗

arXiv2014

Optically induced Aharonov-Bohm effect in mesoscopic rings

We show theoretically that strong electron coupling to circularly polarized photons in non-singly-connected nanostructures results in the appearance of an artificial gauge field that changes the electron phase. The effect arises from the breaking of time-reversal symmetry and is analogous to the well-known Aharonov-Bohm phase effect. It can manifest itself in the oscillations of conductance as a function of the intensity and frequency of the illumination. The theory of the effect is elaborated for mesoscopic rings in both ballistic and diffusive regimes.

cond-mat.mes-hall↗

arXiv2014

Spin-dependent beating patterns in thermoelectric properties: Filtering the carriers of the heat flux in a Kondo adatom system

We theoretically investigate the thermoelectric properties of a spin-polarized two-dimensional electron gas hosting a Kondo adatom hybridized with an STM tip. Such a setup is treated within the single-impurity Anderson model in combination with the atomic approach for the Green's functions. Due to the spin dependence of the Fermi wavenumbers the electrical and thermal conductances, together with thermopower and Lorenz number reveal beating patterns as function of the STM tip position in the Kondo regime. In particular, by tuning the lateral displacement of the tip with respect to the adatom vicinity, the temperature and the position of the adatom level, one can change the sign of the Seebeck coefficient through charge and spin. This opens a possibility of the microscopic control of the heat flux analogously to that established for the electrical current.

cond-mat.str-el↗

arXiv2014

Effect of Inter-Adatoms Correlations on the Local Density of States of Graphene

We discuss theoretically the local density of states (LDOS) of a graphene sheet hosting two distant adatoms located at the center of the hexagonal cells. By putting laterally a Scanning Tunneling Microscope (STM) tip over a carbon atom, two remarkable novel effects can be detected: i) a multilevel structure in the LDOS and ii) beating patterns in the induced LDOS. We show that both phenomena occur nearby the Dirac points and are highly anisotropic. Furthermore, we propose conductance experiments employing STM as a probe for the observation of such exotic manifestations in the LDOS of graphene induced by inter-adatoms correlations.

cond-mat.str-el↗

arXiv2014

Band gaps induced by vacuum photons in closed semiconductor cavities

We consider theoretically a closed (zero-dimensional) semiconductor microcavity where confined vacuum photonic mode is coupled to electrons in valence band of the semiconductor. It is shown that vacuum-induced virtual electron transitions between valence and conduction bands result in renormalization of electron energy spectrum. As a consequence, vacuum-induced band gaps appear within the valence band. Calculated values of the band gaps are of sub-meV scale, that makes this QED effect to be measurable in state-of-the-art experiments.

cond-mat.mes-hall↗

arXiv2014

Superconductivity in Semiconductor Structures: the Excitonic Mechanism

We study theoretically the effect of the fermion and boson densities on the superconductivity transition critical temperature $(T_c)$ of a two dimensional electron gas (2DEG), where superconductivity is mediated by a Bose-Einstein condensate of exciton-polaritons. The critical temperature is found to increase with the boson density, but surprisingly it decreases with the 2DEG density increase. This makes doped semiconductor structures with shallow Fermi energies better adapted for observation of the exciton-induced superconductivity than metallic layers. For the realistic GaAs-based microcavities containing-doped and neutral quantum wells we estimate $T_c$ as close to 50K. Superconductivity is suppressed by magnetic fields of the order of 4T due to the Fermi surface renormalisation.

cond-mat.supr-con↗

arXiv2014

Information processing with topologically protected vortex memories in exciton-polariton condensates

We show that in a non-equilibrium system of an exciton-polariton condensate, where polaritons are generated from incoherent pumping, a ring-shaped pump allows for stationary vortex memory elements of topological charge $m = 1$ or $m = -1$. Using simple potential guides we can choose whether to copy the same charge or invert it onto another spatially separate ring pump. Such manipulation of binary information opens the possibility of a new type processing using vortices as topologically protected memory components.

cond-mat.quant-gas↗

arXiv2014

Semiconductor cavity QED: Bandgap induced by vacuum fluctuations

We consider theoretically a semiconductor nanostructure embedded in one-dimensional microcavity and study the modification of its electron energy spectrum by the vacuum fluctuations of the electromagnetic field. To solve the problem, a non-perturbative diagrammatic approach based on the Green's function formalism is developed. It is shown that the interaction of the system with the vacuum fluctuations of the optical cavity opens gaps within the valence band of the semiconductor. The approach is verified for the case of large photon occupation numbers, proving the validity of the model by comparing to previous studies of the semiconductor system excited by a classical electromagnetic field. The developed theory is of general character and allows for unification of quantum and classical descriptions of the strong light-matter interaction in semiconductor structures.

cond-mat.mes-hall↗

arXiv2014

Tunable single photon emission from dipolaritons

We study a system comprising of a double quantum well embedded in a micropillar optical cavity, where strong coupling between a direct exciton, indirect exciton, and cavity photon is achieved. We show that the resulting hybrid quasiparticles - dipolaritons - can induce strong photon correlations and lead to anti-bunched behaviour of the cavity output field. The origin of the observed single photon emission is attributed to unconventional photon blockade. Moreover, we find that the second-order equal time correlation function $g^{(2)}(0)$ can be tuned over a large range using an electric field applied to the structure, or changing the frequency of the pump. This allows for an on-the-flight control of cavity output properties, and is important for the future generation of tunable single photon emission sources.

cond-mat.mes-hall↗

arXiv2014

Vortices in spinor cold exciton condensates with spin-orbit interaction

We study theoretically the ground states of topological defects in a spinor four-component condensate of cold indirect excitons. We analyze possible ground state solutions for different configurations of vortices and half-vortices. We show that if only Rashba or Dreselhaus spin-orbit interaction (SOI) for electrons is present the stable states of topological defects can represent a cylindrically symmetric half-vortex or half vortex-antivortex pairs, or a non-trivial pattern with warped vortices. In the presence of both of Rashba and Dresselhaus SOI the ground state of a condensate represents a stripe phase and vortex type solutions become unstable.

cond-mat.mes-hall↗

arXiv2013

THz laser based on dipolaritons

We develop the microscopic theory of a terahertz (THz) laser based on the effects of resonant tunneling in a double quantum well heterostructure embedded in both optical and THz cavities. In the strong coupling regime the system hosts dipolaritons, hybrid quasiparticles formed by the direct exciton, indirect exciton and optical photon, which possess large dipole moments in the growth direction. Their radiative coupling to the mode of a THz cavity combined with strong non-linearities provided by exciton-exciton interactions allows for stable emission of THz radiation in the regime of the continuous optical excitation. The optimal parameters for maximizing the THz signal output power are analyzed.

cond-mat.mes-hall↗

arXiv2013

Bistability in Microcavities with Incoherent Optical or Electrical Excitation

We consider a quantum well embedded in a zero-dimensional microcavity with a sub-wavelength grated mirror, where the x-linearly polarized exciton mode is strongly coupled to the cavity photon, while y-polarized excitons remain in the weak coupling regime. Under incoherent optical or electric pumping, we demonstrate polariton bistability associated with parametric scattering processes. Such bistability is useful for constructing polaritonic devices with optical or electrical incoherent pumping.

cond-mat.mes-hall↗

arXiv2013

Superradiant terahertz emission by dipolaritons

Dipolaritons are mixed light-matter quasiparticles formed in double quantum wells embedded in microcavities. Due to resonant coupling between direct and indirect excitons via electronic tunnelling, dipolaritons possess large dipole moments. Resonant excitation of the cavity mode by a short pulse of light induces oscillations of the indirect exciton density with a characteristic frequency of Rabi flopping. This results in oscillations of classical Hertz dipoles array which generate supperradiant emission on a terahertz (THz) frequency. Resulting THz signal may be enhanced using the supplementary THz cavity in the weak coupling regime.

cond-mat.mes-hall↗

arXiv2013

Phase diagrams of magnetopolariton gases

The magnetic field effect on phase transitions in electrically neutral bosonic systems is much less studied than those in fermionic systems, such as superconducting or ferromagnetic phase transitions. Nevertheless, composite bosons are strongly sensitive to magnetic fields: both their internal structure and motion as whole particles may be affected. A joint effort of ten laboratories has been focused on studies of polariton lasers, where non-equilibrium Bose-Einstein condensates of bosonic quasiparticles, exciton-polaritons, may appear or disappear under an effect of applied magnetic fields. Polariton lasers based on pillar or planar microcavities were excited both optically and electrically. In all cases a pronounced dependence of the onset to lasing on the magnetic field has been observed. For the sake of comparison, photon lasing (lasing by an electron-hole plasma) in the presence of a magnetic field has been studied on the same samples as polariton lasing. The threshold to photon lasing is essentially governed by the excitonic Mott transition which appears to be sensitive to magnetic fields too. All the observed experimental features are qualitatively described within a uniform model based on coupled diffusion equations for electrons, holes and excitons and the Gross-Pitaevskii equation for exciton-polariton condensates. Our research sheds more light on the physics of non-equilibrium Bose-Einstein condensates and the results manifest high potentiality of polariton lasers for spin-based quantum logic applications.

cond-mat.mes-hall↗