arXiv subjects

Alexey Kavokin

Publications and source records attributed to Alexey Kavokin.

52 records · Page 3Linked to original sources

arXiv2019

Magnetic field induced splitting and polarization of monolayer-based valley exciton-polaritons

Atomically thin crystals of transition metal dichalcogenides are ideally suited to study the interplay of light-matter coupling, polarization and magnetic field effects. In this work, we investiagte the formation of exciton-polaritons in a MoSe2 monolayer, which is integrated in a fully-grown, monolithic microcavity. Due to the narrow linewidth of the polaritonic resonances, we are able to directly investigate the emerging valley Zeeman splitting of the hybrid light-matter resonances in the presence of a magnetic field. At a detuning of -54.5 meV (13.5 % matter constituent of the lower polariton branch), we find a Zeeman splitting of the lower polariton branch of 0.36 meV, which can be directly associated with an excitonic g factor of 3.94\pm0.13. Remarkably, we find that a magnetic field of 6T is sufficient to induce a notable valley polarization of 15 % in our polariton system, which approaches 30% at 9T. Strikingly, this circular polarization degree of the polariton (ground) state exceeds the polarization of the exciton reservoir for equal magnetic field magnitudes by approximately 50%, as a consequence of enhanced relaxation of bosons in our monolayer-based system.

cond-mat.mes-hall↗

arXiv2018

Magnetic control of polariton spin transport

We show the full control of the polarization dynamics of a propagating exciton-polariton condensate in a planar microcavity by using a magnetic field applied in the Voigt geometry. The change of the spin-beat frequency, the suppression of the optical spin Hall effect and the rotation of the polarization pattern by the magnetic field are theoretically reproduced by accounting for the magneto-induced mixing of exciton-polariton and dark, spin forbidden, exciton states.

cond-mat.quant-gas↗

arXiv2018

Self-trapping of exciton-polariton condensates

The self-trapping of exciton-polariton condensates is demonstrated and explained by the formation of a new polaron-like state. Above the polariton lasing threshold, local variation of the lattice temperature provides the mechanism for an attractive interaction between polaritons. Due to this attraction, the condensate collapses into a small bright spot. Its position and momentum variances approach the Heisenberg quantum limit. The self-trapping does not require either a resonant driving force or a presence of defects. The trapped state is stabilized by the phonon-assisted stimulated scattering of excitons into the polariton condensate. While the formation mechanism of the observed self-trapped state is similar to the Landau-Pekar polaron model, this state is populated by several thousands of quasiparticles, in a strike contrast to the conventional single-particle polaron state.

cond-mat.quant-gas↗

arXiv2018

The laser synthesis of linear carbon chains

We synthesize macroscopically long linear carbon chains (carbynes) in a colloidal solution, then deposit them on a surface. The method is based on the formation of carbon threads by laser ablation in a colloid accompanied by the stabilization of resulting linear carbon chains by golden nanoparticles. We observe the signatures of the polyyne allotrope of carbyne in the photoluminescence and Raman spectra of the solutions. We deposit the synthesized carbyne threads on fused quartz glass substrates. The transmission electron microscopy images of the deposited threads with golden nanoparticles attached to their ends demonstrate the straight linear parts of the monoatomic carbon chains varying in length between 8 and 24 carbon atoms. This method paves the way to fabrication of an ultimate one-dimensional crystal: a monoatomic carbon wire.

physics.atm-clus↗

arXiv2018

Dynamics of liquid crystal on hexagonal lattice

Nematic liquid crystal (LC) molecules adsorbed on two dimensional materials are aligned along the crystal directions of the hexagonal lattice. It was demonstrated that short electric pulses can reorient the aligned LC molecules in the preferred armchair direction of hexagonal boron nitride (h-BN). Several states with a variety of colors were obtained by changing the direction and strength of the electric pulses. The ab initio calculations based on density functional theory was carried out to determine the favorable adsorption configurations of the LC molecules on the h-BN surface. A non-volatile display, in which pixel resolution can be determined by grains of hexagonal surface, is proposed, which can offer a pathway towards dynamic high-quality pixels with low power consumption, and could define a new paradigm for all non-volatile display applications.

cond-mat.soft↗

arXiv2018

Non-Linear Photocurrent Response to Bosonic Final State Stimulation in Microcavity Diodes

We report the optical excitation-dependent output photocurrent characteristics of GaN-based polariton diode lasers operated under reverse-bias at room temperature. The photocurrent demonstrates a non-linear enhancement at an incident optical power of ~ 1.6 mW, which is approximately equivalent to the value of polariton lasing threshold observed when the diodes are operated under forward bias conditions. This is explained in the framework of an Auger-like process of excitonic dissociation into its constituent electron-hole pairs, which can be stimulated by the occupation of the polariton lasing states. The observed effect is a remarkable manifestation of the bosonic final state stimulation in polariton lasers. A model based on the coupled kinetic equations for the free carriers, the excitonic reservoir and the polariton condensate shows a good agreement to the experimental data.

physics.app-ph↗

arXiv2017

Dynamics of the Optical Spin Hall Effect

We study the time evolution of the Optical Spin Hall Effect (OSHE), which occurs when exciton-polaritons undergo resonant Rayleigh scattering. The resulting spin pattern in momentum space is quantified by calculating the degree of circular polarization of the momentum space image for each point in time. We find the degree of circular polarization performing oscillations, which can be described within the framework of the pseudospin model by Kavokin et al. (Ref. 1).

cond-mat.mes-hall↗

arXiv2017

Observation of hybrid Tamm-plasmon exciton-polaritons with GaAs quantum wells and a MoSe2 monolayer

Strong light matter coupling between excitons and microcavity photons, as described in the framework of cavity quantum electrodynamics, leads to the hybridization of light and matter excitations. The regime of collective strong coupling arises, when various excitations from different host media are strongly coupled to the same optical resonance. This leads to a well-controllable admixture of various matter components in three hybrid polariton modes. Here, we study a cavity device with four embedded GaAs quantum wells hosting excitons that are spectrally matched to the A-valley exciton resonance of a MoSe2 monolayer. The formation of hybrid polariton modes is evidenced in momentum resolved photoluminescence and reflectivity studies. We describe the energy and k-vector distribution of exciton-polaritons along the hybrid modes by a thermodynamic model, which yields a very good agreement with the experiment.

cond-mat.quant-gas↗

arXiv2015

Second-order correlations in an exciton-polariton Rabi oscillator

We develop the theoretical formalism to calculate second-order correlations in dissipative exciton-polariton system and we propose intensity-intensity correlation experiments to reveal the physics of exciton-light coupling in semiconductor microcavities in the Rabi oscillation regime. We predict a counter intuitive behaviour of the correlator between upper and lower polariton branches: due to the decoherence caused by stochastic exciton-photon conversions this correlator is expected to decrease below 1, while the individual second-order coherence of upper and lower polaritons exhibits non-monotonous bunching.

cond-mat.mes-hall↗

arXiv2015

Ghost Branch Photoluminescence From a Polariton Fluid Under Nonresonant Excitation

An expanding polariton condensate is investigated under pulsed nonresonant excitation with a small laser pump spot. Far above the condensation threshold we observe a pronounced increase in the dispersion curvature with a subsequent linearization of the spectrum and strong luminescence from a ghost branch orthogonally polarized with respect to the linearly polarized condensate emission. The presence of the ghost branch has been confirmed in time-resolved measurements. The dissipative and nonequilibrium effects in the photoluminescence of polariton condensates and their excitations are discussed.

cond-mat.mes-hall↗

arXiv2015

Exciton-polaritons in 2D dichalcogenide layers placed in a planar microcavity: tuneable interaction between two Bose-Einstein condensates

Exciton-polariton modes arising from interaction between bound excitons in monolayer thin semiconductor sheets and photons in a Fabry-Perot microcavity are considered theoretically. We calculate the dispersion curves, mode lifetimes, Rabi splitting, and Hopfield coefficients of these structures for two nearly 2D semiconductor materials, MoS2 and WS2, and suggest that they are interesting for studying the rich physics associated with the Bose-Einstein condensation of exciton-polaritons. The large exciton binding energy and dipole allowed exciton transitions, in addition to the relatively easily controllable distance between the semiconductor sheets are the advantages of this system in comparison with traditional GaAs or CdTe based semiconductor microcavities. In particular, in order to mimic the rich physical properties of the quantum degenerate mixture of two bosonic species of dilute atomic gases with tunable inter-species interaction , we put forward a structure containing two semiconductor sheets separated by some atomic-scale distance (l) using a nearly 2D dielectric (e.g. h-BN), which offers the possibility of tuning the interaction between two exciton-polariton Bose-Enstein condensates. We show that the dynamics of this novel structure are ruled by two coupled Gross-Pitaevskii equations with the coupling parameter proportional to 1/l.

cond-mat.mes-hall↗

arXiv2015

Hyperbolic Metamaterials with Bragg Polaritons

We propose a novel mechanism for designing quantum hyperbolic metamaterials with use of semi-conductor Bragg mirrors containing periodically arrangedquantum wells. The hyperbolic dispersion of exciton-polariton modes is realized near the top of the first allowed photonic miniband in such structure which leads to formation of exciton-polariton X-waves. Exciton-light coupling provides a resonant non-linearity which leads to non-trivial topologic solutions. We predict formation of low amplitude spatially localized oscillatory structures: oscillons described by kink shaped solutions of the effective Ginzburg-Landau-Higgs equation. The oscillons have direct analogies in the gravita-tional theory. We discuss implementation of exciton-polariton Higgs fields for the Schrodinger cat state generation.

cond-mat.mes-hall↗

arXiv2013

Prediction of thermomagnetic and thermoelectric properties for novel materials and systems

We express the link between conductivity and coefficients of Seebeck, Nernst-Ettingshausen, Peltier, and Thompson and Reghi-Leduc via the temperature derivative of the chemical potential of a system. These general expressions are applied to three-, two- and one-dimensional systems of charge carriers having a parabolic or Dirac spectrum. The method allows for predicting thermoelectric and thermomagnetic properties of novel materials and structures.

cond-mat.mes-hall↗

arXiv2011

THz lasing in a polariton system: Quantum theory

We study the laser regime of terahertz (THz) emission from a semiconductor microcavity in the strong coupling regime, where optical transitions between upper and lower exciton-polariton modes are allowed due to the mixing of the upper mode with one of the dark exciton states. Using a system of master-Boltzmann equations describing both polariton modes and the THz mode, we calculate the first and second order coherences and the spectral shape of THz emission. This analysis shows that THz lasing in microcavities is possible provided that the system is embedded in a good THz cavity, that the optical (polariton) lasing condition is fulfilled and if the depletion of the upper polariton mode due to acoustic phonon assisted relaxation processes is reduced. This latter condition is likely to be realised in pillar microcavities, which seem to be the most suitable candidates for realisation of a THz laser.

cond-mat.mes-hall↗

arXiv2010

Exciton-polariton mediated superconductivity

We revisit the exciton mechanism of superconductivity in the framework of microcavity physics, replacing virtual excitons as a binding agent of Cooper pairs by excitations of an exciton-polariton Bose-Einstein condensate. We consider a model microcavity where a quantum well with a two dimensional electron gas is sandwiched between two undoped quantum wells, where a polariton condensate is formed. We show that the critical temperature for superconductivity dramatically increases with the condensate population, opening a new route towards high temperature superconductivity.

cond-mat.supr-con↗

arXiv2005

Multiplets in Emission of Large Quantum Dots in Microcavities

We show theoretically that the emission spectrum of a single large quantum dot strongly coupled to a single photon mode in a microcavity can be qualitatively different from the spectrum obtained with an atom in a cavity. Instead of the well-known Mollow triplet we predict appearance of multiplets with the number of peaks a function of the quantum dot size and pumping intensity. The mutiplets can appear if the quantum dot is larger than the exciton Bohr radius, so that excitons are confined as whole particles in the dot. In this case the Pauli principle is relaxed and one can accommodate more than one exciton (but still a finite number) in a given quantum state.

cond-mat.mes-hall↗