arXiv subjects

A. Kavokin

Publications and source records attributed to A. Kavokin.

13 recordsLinked to original sources

arXiv2026

Probing intermittent polariton vortex dynamics with two-point correlations

Superconducting single-photon detectors with time resolution of 80 ps have been used to study the spatiotemporal dynamics of a trapped bosonic condensate of exciton-polaritons. Both second- and first-order correlation functions are found to exhibit pronounced oscillations in time governed by the dynamics of the polariton condensate in the trap. We have identified the intermittent regime of stochastic transitions between stationary and limit-cycle regimes near the Andronov-Hopf bifurcation manifested in asymmetric distortions of the correlation function. This rich interplay of deterministic and stochastic condensate dynamics is explained theoretically as a manifestation of mutually compensating self-repulsion and reservoir-mediated attraction.

cond-mat.mes-hall↗

arXiv2026

Collective Excitations and Stability of Nonequilibrium Polariton Supersolids

Formation of nonequilibrium counterparts of supersolids, simultaneously characterized with spontaneous superfluid and crystalline order, was recently reported in incoherently pumped polariton condensates. We investigate collective excitation spectra of this phase and explicitly demonstrate the emergence of gapless Nambu-Goldstone modes due to spontaneously broken continuous phase and translation symmetries. For the recent implementation of the polariton nonequilibrium supersolidity in semiconductor metasurfaces [D. Trypogeorgos et al., Nature 639, 337 (2025)], we demonstrate the key role of attractive polariton interactions, mediated by the excitonic reservoir, for stability of the supersolid phase. Performing a thorough numerical investigation, we identify the conditions for existence of the diagonal and off-diagonal long-range order in negative-mass nonequilibrium supersolids.

cond-mat.mes-hall↗

arXiv2021

Dissipative Josephson vortices in annular polariton fluids

We consider two concentric rings formed by bosonic condensates of exciton-polaritons. A circular superfluid flow of polaritons in one of the rings can be manipulated by acting upon the second annular polariton condensate. The complex coupling between the rings with different topological charges triggers nucleation of stable Josephson vortices (JVs) which are revealed as topological defects of the angular dependence of the relative phase between rings. Being dependent on the coupling strength, the structure of the JV governs the difference of the mean angular momenta of the inner and the outer rings. At the vanishing coupling the condensates rotate independently demonstrating no correlations of their winding numbers. At the moderate coupling, the interaction between two condensates tends to equalize their mean angular momenta despite of the mismatch of the winding numbers demonstrating the phenomenology of a drag effect. Above the critical coupling strength the synchronous rotation is established via the phase slip events.

cond-mat.quant-gas↗

arXiv2021

Pseudo-conservative dynamics of coupled polariton condensates

Open-dissipative systems obeying parity-time ($\mathcal{PT}$) symmetry are capable of demonstrating oscillatory dynamics akin to the conservative systems. In contrast to limit cycle solutions characteristic of nonlinear systems, the $\mathcal{PT}$-symmetric oscillations form a continuum of non-isolated orbits. However, precise sculpturing of the real potential and the gain-loss spatial profiles required for establishing of the $\mathcal{PT}$-symmetry is practically challenging. The optical devices, such as lasers, exhibit relaxation dynamics and do not operate as the $\mathcal{PT}$-symmetric systems. Here we demonstrate how these constraints can be overcome. We predict that a pair of optically trapped polariton condensates (a polariton dimer) can be excited and operated in the oscillating regime typical of the isolated systems. This regime can be realized in the presence of both dissipative and conservative coupling between the condensates and can be maintained at an arbitrary external pump intensity. Every orbit is characterised by a frequency comb appearing in the spectrum of a dimer in the presence of the conservative nonlinearity. Our results pave the way for the creation of the optical computing devices operating under the constant-wave external pumping.

cond-mat.mes-hall↗

arXiv2018

Superlinear Increase of Photocurrent due to Stimulated Scattering into a Polariton Condensate

We show that when a monopolar current is passed through an n-i-n structure, superlinear photocurrent response occurs when there is a polariton condensate. This is in sharp contrast to the previously observed behavior for a standard semiconductor laser. Theoretical modeling shows that this is due to a stimulated exciton-exciton scattering process in which one exciton relaxes into the condensate, while another one dissociates into an electron-hole pair.

cond-mat.quant-gas↗

arXiv2017

The interplay between excitons and trions in a monolayer of MoSe$_2$

We study the impact of a free carrier reservoir on the optical properties of excitonic and trionic complexes in a MoSe$_2$ monolayer at cryogenic temperatures. By applying photodoping via a non-resonant pump laser the electron density can be controlled in our sample and in turn the exciton and trion densities can be tuned. We find a significant increase of the trion binding energy in the presence of an induced electron gas both in power- and in time-resolved photoluminescence spectra. This behaviour is reproduced within the original variational approach that takes into account both screening and phase space filling effects.

cond-mat.mes-hall↗

arXiv2015

Real-space collapse of a polariton condensate

Polaritons in microcavities are versatile quasi-2D bosonic particles with a high degree of coherence and strong nonlinearities, thanks to their hybrid light-matter character. In their condensed form, they display striking quantum hydrodynamic features analogous to atomic Bose-Einstein condensates, such as long-range order coherence, superfluidity and quantized vorticity. Their variegated dispersive and dissipative properties, however, set significant differences from their atomic counterpart. In this work, we report the unique phenomenology that is observed when a pulse of light impacts the polariton vacuum: the condensate that is instantaneously formed does not splash in real space but instead coheres into an enigmatic structure, featuring concentric rings and, most notably, a sharp and bright peak at the center. Using a state-of-the-art ultrafast imaging with 50 fs time steps, we are able to track the dynamics of the polariton mean-field wavefunction in both real and reciprocal space. The observation of the real-space collapse of the condensate into an extremely localized---resolution limited---peak is at odd with the repulsive interactions of polaritons and their positive effective mass. An unconventional mechanism is therefore at play to account for our observations. Our modeling suggests that self-trapping due to a local heating of the crystal lattice---that can be described as a collective polaron formed by a polariton condensate---could be involved. These observations hint at the fascinating fluid dynamics of polaritons in conditions of extreme intensities and ultrafast times.

cond-mat.quant-gas↗

arXiv2014

Excited states of exciton-polariton condensates in 2D and 1D harmonic traps

We present a theoretical description of Bogolyubov-type excitations of exciton-polariton Bose-Einstein condensates (BECs) in semiconductor microcavities. For a typical two dimensional (2D) BEC we focus on two limiting cases, the weak- and strong-coupling regimes, where a perturbation theory and the Thomas-Fermi approximation, respectively, are valid. We calculate integrated scattering intensity spectra for probing the collective excitations of the condensate in both considered limits. Moreover, in relation to recent experiments on optical modulation allowing localization of condensates in a trap with well controlled shape and dimensions, we study the quasi-one dimensional (1D) motion of the BEC in microwires and report the corresponding Bogolyubov's excitation spectrum. We show that in 1D case the characteristic polariton-polariton interaction constant is expressed as $g_{1}=3λ\mathcal{N}/(2L_{y})$ ($λ$ is the 2D polariton-polaritons interaction parameter in the cavity, $\mathcal{N}$ the number of the particles, and $L_{y}$ the wirecavity width). We reveal some interesting features for 2D and 1D Bogolyubov spectra for both repulsive $(λ>0)$ and attractive $(λ<0)$ interaction.

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↗

arXiv2013

Motion of spin polariton bullets in semiconductor microcavities

The dynamics of optical switching in semiconductor microcavities in the strong coupling regime is studied using time- and spatially-resolved spectroscopy. The switching is triggered by polarised short pulses which create spin bullets of high polariton density. The spin packets travel with speeds of the order of 106 m/s due to the ballistic propagation and drift of exciton-polaritons from high to low density areas. The speed is controlled by the angle of incidence of the excitation beams, which changes the polariton group velocity.

cond-mat.mes-hall↗

arXiv2008

Spin transport of indirect excitons in GaAs coupled quantum wells

Spin transport of indirect excitons in GaAs/AlGaAs coupled quantum wells was observed by measuring the spatially resolved circular polarization of the exciton emission. The exciton spin transport originates from the long spin relaxation time and long lifetime of the indirect excitons.

cond-mat.mes-hall↗

arXiv2007

Resonant light delay in GaN with ballistic and diffusive propagation

We report on a strong delay in light propagation through bulk GaN, detected by time-of-flight spectroscopy. The delay increases resonantly as the photon energy approaches the energy of a neutral-donor bound exciton (BX), resulting in a velocity of light as low as 2100 km/s. In the close vicinity of the BX resonance, the transmitted light contains both ballistic and diffusive components. This phenomenon is quantitatively explained in terms of optical dispersion in a medium where resonant light scattering by the BX resonance takes place in addition to the polariton propagation.

cond-mat.mtrl-sci↗

arXiv2003

Mie-resonances, infrared emission and band gap of InN

Mie resonances due to scattering/absorption of light in InN containing clusters of metallic In may have been erroneously interpreted as the infrared band gap absorption in tens of papers. Here we show by direct thermally detected optical absorption measurements that the true band gap of InN is markedly wider than currently accepted 0.7 eV. Micro-cathodoluminescence studies complemented by imaging of metallic In have shown that bright infrared emission at 0.7-0.8 eV arises from In aggregates, and is likely associated with surface states at the metal/InN interfaces.

cond-mat.mtrl-sci↗