arXiv subjects

C. Brimont

Publications and source records attributed to C. Brimont.

14 recordsLinked to original sources

arXiv2026

Mode-locking instability and multiple soliton formation in GaN polariton waveguide cavities

We study the emergence of multi-soliton regimes in 1D ridge polariton waveguides of two different lengths. We show that by varying the position of the gain, which in out-of-equilibrium polariton systems is provided by the pumping laser and its associated excitonic reservoir, it is possible to tune the regime of soliton formation between single and multiple solitons. This soliton dynamics can be quantitatively reproduced by solving the Gross-Pitaevskii equations of the coupled exciton-photon system, which show that the soliton splitting mechanism is governed by the exciton reservoir dynamics.

cond-mat.mes-hall↗

arXiv2025

Soliton formation in a bound state in the continuum GaN waveguide polariton laser

We study polaritonic bound states in the continuum (BIC) created in GaN waveguides. The existence of symmetry-protected BICs is confirmed by the suppression of light emission and the observation of a polarization vortex in momentum space. Upon increasing the pumping, polariton population accumulates at the BIC and we observe polariton lasing from the blueshifted BIC states. The assessment of the polariton BIC emission energy and of its real and momentum space wavefunctions as a function of pumping power, i.e. of polariton density, indicates the formation of a bright soliton above the lasing threshold. Soliton formation at the BIC is induced by the combination of negative mass BIC and of repulsive polariton-polariton and polariton-reservoir interactions.

cond-mat.mes-hall↗

arXiv2023

Mode-locked GaN waveguide polariton laser

So far, exciton-polariton (polariton) lasers were mostly single mode lasers based on microcavities. Despite the large repulsive polariton-polariton interaction, pulsed mode-locked polariton laser was never reported. Here, we use a $60 \ \mu m-$long GaN-based waveguide surrounded by distributed Bragg reflectors forming a multi-mode horizontal cavity. We demonstrate experimentally and theoretically a polariton mode-locked micro-laser operating in the blue-UV, at room temperature, with a 300$\ GHz$ repetition rate and 100$\ fs$-long pulses. The mode locking is demonstrated by the compensation (linearization) of the mode dispersion by the self-phase modulation induced by the polariton-polariton interaction. It is also supported by the observation in experiment and theory of the typical envelope frequency profile of a bright soliton.

physics.optics↗

arXiv2023

Electrostatic modulation of excitonic fluid in GaN/AlGaN quantum wells by deposition of few-layered graphene and nickel/gold films

Excitons hosted by GaN/(Al,Ga)N quantum wells (QWs) are spatially indirect due to the giant built-in electric field that separates electrons and holes along the growth direction. This electric field, and thus exciton energy, can be reduced by depositing metallic layers on the sample surface. Using spatially-resolved micro-photoluminescence spectroscopy we compare the effects of two different materials, Nickel/Gold (NiAu) and few-layered graphene (FLG), on the potential landscape experienced by the excitons. We are able to (i) determine the potential barriers imposed on QW excitons by deposition of FLG and NiAu to be $14$ and $82$~meV, respectively, and (ii) to evidence their impact on the exciton transport at appropriate densities. Optical losses and inhomogeneous broadening induced by deposition of NiAu and FLG layers are similar, and their joined implementation constitute a promising tool for electrostatic modulation of IX densities even in the absence of any applied electric bias.

cond-mat.quant-gas↗

arXiv2022

Electrical control of excitons in GaN/(Al,Ga)N quantum wells

A giant built-in electric field in the growth direction makes excitons in wide GaN/(Al, Ga)N quantum wells spatially indirect even in the absence of any external bias. Significant densities of indirect excitons can accumulate in electrostatic traps imprinted in the quantum well plane by a thin metal layer deposited on top of the heterostructure. By jointly measuring spatially-resolved photoluminescence and photo-induced current, we demonstrate that exciton density in the trap can be controlled via an external electric bias, which is capable of altering the trap depth. Application of a negative bias deepens the trapping potential, but does not lead to any additional accumulation of excitons in the trap. This is due to exciton dissociation instigated by the lateral electric field at the electrode edges. The resulting carrier losses are detected as an increased photo-current and reduced photoluminescence intensity. By contrast, application of a positive bias washes out the electrode-induced trapping potential. Thus, excitons get released from the trap and recover free propagation in the plane that we reveal by spatially-resolved photoluminescence.

cond-mat.quant-gas↗

arXiv2020

Strong coupling of exciton-polaritons in a bulk GaN planar waveguide: quantifiying the coupling strength

We investigate the demonstration and quantification of the strong coupling between excitons and guided photons in a GaN slab waveguide. The dispersions of waveguide polaritons are measured from T=6~K to 300~K through gratings. They are carefully analyzed within four models based on different assumptions, in order to assess the strong coupling regime. We prove that the guided photons and excitons are strongly coupled at all investigated temperatures, with a small $(11 \%)$ dependence on the temperature. However the values of the Rabi splitting strongly vary among the four models: the "coupled oscillator" model over-estimates the coupling; the analytical "Elliott-Tanguy" model precisely describes the dielectric susceptibility of GaN near the excitonic transition, leading to a Rabi splitting equal to $82 \pm 10 \ meV$ for TE0 modes; the experimental ellipsometry-based model leads to smaller values of $55 \pm 6 \ meV.$ We evidence that for waveguides including active layers with large oscillator strengths, as required for room-temperature polaritonic devices, a strong bending of the modes dispersion is not necessarily the signature of the strong-coupling, which requires for its reliable assessment a precise analysis of the material dielectric susceptibility.

cond-mat.mes-hall↗

arXiv2020

Complexity of dipolar exciton Mott transition in GaN/(AlGa)N nanostructures

The Mott transition from a dipolar excitonic liquid to an electron-hole plasma is demonstrated in a wide GaN/(Al,Ga)N quantum well at $T=7$K by means of spatially-resolved magneto-photoluminescence spectroscopy. Increasing optical excitation density we drive the system from the excitonic state, characterized by a diamagnetic behavior and thus a quadratic energy dependence on the magnetic field, to the unbound electron-hole state, characterized by a linear shift of the emission energy with the magnetic field. The complexity of the system requires to take into account both the density-dependence of the exciton binding energy and the exciton-exciton interaction and correlation energy that are of the same order of magnitude. We estimate the carrier density at Mott transition as $n_\mathrm{Mott}\approx 2\times 10^{11}$cm$^{-2}$ and address the role played by excitonic correlations in this process. Our results strongly rely on the spatial resolution of the photoluminescence and the assessment of the carrier transport. We show, that in contrast to GaAs/(Al,Ga)As systems, where transport of dipolar magnetoexcitons is strongly quenched by the magnetic field due to exciton mass enhancement, in GaN/(Al,Ga)N the band parameters are such that the transport is preserved up to $9$T.

cond-mat.mes-hall↗

arXiv2019

Dipolar excitons offer a rich playground for both design of novel optoelectronic devices and fundamental many-body physics

Dipolar excitons offer a rich playground for both design of novel optoelectronic devices and fundamental many-body physics. Wide GaN/(AlGa)N quantum wells host a new and promising realization of dipolar excitons. We demonstrate the in-plane confinement and cooling of these excitons, when trapped in the electrostatic potential created by semitransparent electrodes of various shapes deposited on the sample surface. This result is a prerequisite for the electrical control of the exciton densities and fluxes, as well for studies of the complex phase diagram of these dipolar bosons at low temperature.

physics.app-ph↗

arXiv2019

Competition between horizontal and vertical polariton lasing in planar microcavities

Planar microcavities filled with active materials containing excitonic resonances host radiative exciton-polariton (polariton) modes with in-plane wave vectors within the light cone. They also host at least one mode guided in the cavity plane by total internal reflection and which is not radiatively coupled to the vacuum modes except through defects or sample edges. We show that polariton lasing mediated by polariton stimulated scattering can occur concomitantly in both types of modes in a microcavity. By adjusting the detuning between the exciton and the radiative photon mode one can favor polariton lasing either in the radiative or in the guided modes. Our results suggest that the competition between these two types of polariton lasing modes may have played a role in many previous observations of polariton lasing and polariton Bose Einstein condensation.

cond-mat.mes-hall↗

arXiv2016

Room-temperature transport of indirect excitons in (Al,Ga)N/GaN quantum wells

We report on the exciton propagation in polar (Al,Ga)N/GaN quantum wells over several micrometers and up to room temperature. The key ingredient to achieve this result is the crystalline quality of GaN quantum wells (QWs) grown on GaN template substrate. By comparing microphotoluminescence images of two identical QWs grown on sapphire and on GaN, we reveal the twofold role played by GaN substrate in the transport of excitons. First, the lower threading dislocation densities in such structures yield higher exciton radiative efficiency, thus limiting nonradiative losses of propagating excitons. Second, the absence of the dielectric mismatch between the substrate and the epilayer strongly limits the photon guiding effect in the plane of the structure,making exciton transport easier to distinguish from photon propagation. Our results pave the way towards room-temperature gate-controlled exciton transport in wide-bandgap polar heterostructures.

cond-mat.mes-hall↗

arXiv2015

Transport of dipolar excitons in (Al,Ga)N/GaN quantum wells

We investigate the transport of dipolar indirect excitons along the growth plane of polar (Al,Ga)N/GaN quantum well structures by means of spatially- and time-resolved photoluminescence spectroscopy. The transport in these strongly disordered quantum wells is activated by dipole-dipole repulsion. The latter induces an emission blue shift that increases linearly with exciton density, whereas the radiative recombination rate increases exponentially. Under continuous, localized excitation, we measure a continuous red shift of the emission, as excitons propagate away from the excitation spot. This shift corresponds to a steady-state gradient of exciton density, measured over several tens of micrometers. Time-resolved micro-photoluminescence experiments provide information on the dynamics of recombination and transport of dipolar excitons. We account for the ensemble of experimental results by solving the nonlinear drift-diffusion equation. Quantitative analysis suggests that in such structures, exciton propagation on the scale of 10 to 20 microns is mainly driven by diffusion, rather than by drift, due to the strong disorder and the presence of nonradiative defects. Secondary exciton creation, most probably by the intense higher-energy luminescence, guided along the sample plane, is shown to contribute to the exciton emission pattern on the scale up to 100 microns. The exciton propagation length is strongly temperature dependent, the emission being quenched beyond a critical distance governed by nonradiative recombination.

cond-mat.quant-gas↗

arXiv2014

Patterned silicon substrates: a common platform for room temperature GaN and ZnO polariton lasers

A new platform for fabricating polariton lasers operating at room temperature is introduced: nitride-based distributed Bragg reflectors epitaxially grown on patterned silicon substrates. The patterning allows for an enhanced strain relaxation thereby enabling to stack a large number of crack-free AlN/AlGaN pairs and achieve cavity quality factors of several thousands with a large spatial homogeneity. GaN and ZnO active regions are epitaxially grown thereon and the cavities are completed with top dielectric Bragg reflectors. The two structures display strong-coupling and polariton lasing at room temperature and constitute an intermediate step in the way towards integrated polariton devices.

cond-mat.mes-hall↗

arXiv2011

LO-phonon assisted polariton lasing in a ZnO based microcavity

Polariton relaxation mechanisms are analysed experimentally and theoretically in a ZnO-based polariton laser. A minimum lasing threshold is obtained when the energy difference between the exciton reservoir and the bottom of the lower polariton branch is resonant with the LO phonon energy. Tuning off this resonance increases the threshold, and exciton-exciton scattering processes become involved in the polariton relaxation. These observations are qualitatively reproduced by simulations based on the numerical solution of the semi-classical Boltzmann equations.

cond-mat.mtrl-sci↗

arXiv2011

Fabrication and Optical Properties of a Fully Hybrid Epitaxial ZnO-Based Microcavity in the Strong Coupling Regime

In order to achieve polariton lasing at room temperature, a new fabrication methodology for planar microcavities is proposed: a ZnO-based microcavity in which the active region is epitaxially grown on an AlGaN/AlN/Si substrate and in which two dielectric mirrors are used. This approach allows as to simultaneously obtain a high-quality active layer together with a high photonic confinement as demonstrated through macro-, and micro-photoluminescence (μ-PL) and reflectivity experiments. A quality factor of 675 and a maximum PL emission at k=0 are evidenced thanks to μ-PL, revealing an efficient polaritonic relaxation even at low excitation power.

cond-mat.mtrl-sci↗