I will discuss here our results on phonon-assisted recombination in hBN, from bulk crystals to few-layer samples. First, I will focus on hBN crystals where the combination of isotopic purification, Raman scattering and polarized-resolved photoluminescence allowed us to identify the different phonon modes involved in the efficient phonon-assisted recombination in bulk hBN. In a second part, I will discuss photoluminescence experiments in epilayers grown by high-temperature molecular beam epitaxy. These epilayers have a thickness of few monolayers of hBN, and I will show that phonon-assisted recombination displays a distinct phenomenology with a PL spectrum different from the one of bulk crystals.

I will discuss here our results on phonon-assisted recombination in hBN, from bulk crystals to few-layer samples. First, I will focus on hBN crystals where the combination of isotopic purification, Raman scattering and polarized-resolved photoluminescence allowed us to identify the different phonon modes involved in the efficient phonon-assisted recombination in bulk hBN. In a second part, I will discuss photoluminescence experiments in epilayers grown by high-temperature molecular beam epitaxy. These epilayers have a thickness of few monolayers of hBN, and I will show that phonon-assisted recombination displays a distinct phenomenology with a PL spectrum different from the one of bulk crystals.

I will discuss here our results on phonon-assisted recombination in hBN, from bulk crystals to few-layer samples. First, I will focus on hBN crystals where the combination of isotopic purification, Raman scattering and polarized-resolved photoluminescence allowed us to identify the different phonon modes involved in the efficient phonon-assisted recombination in bulk hBN. In a second part, I will discuss photoluminescence experiments in epilayers grown by high-temperature molecular beam epitaxy. These epilayers have a thickness of few monolayers of hBN, and I will show that phonon-assisted recombination displays a distinct phenomenology with a PL spectrum different from the one of bulk crystals.

I will discuss here our results on phonon-assisted recombination in hBN, from bulk crystals to few-layer samples. First, I will focus on hBN crystals where the combination of isotopic purification, Raman scattering and polarized-resolved photoluminescence allowed us to identify the different phonon modes involved in the efficient phonon-assisted recombination in bulk hBN. In a second part, I will discuss photoluminescence experiments in epilayers grown by high-temperature molecular beam epitaxy. These epilayers have a thickness of few monolayers of hBN, and I will show that phonon-assisted recombination displays a distinct phenomenology with a PL spectrum different from the one of bulk crystals.

We study shallow and deep levels in carbon-doped hexagonal boron nitride crystals precipitated from a molten metal solution in a high-temperature furnace. Reflectance and photoluminescence under deep ultraviolet excitation are complemented by spatially resolved experiments by means of a scanning confocal micro-photoluminescence setup operating in the ultraviolet. Isotopically controlled carbon doping does not induce any energy shift of the well-known deep-level emission at 4.1 eV. Our detailed characterization in a series of carbon-doped crystals reveals that the incorporation of carbon during the growth process results in a distinct class of shallow and deep levels in hexagonal boron nitride, calling into question the exact role of carbon in the growth of hexagonal boron nitride and its direct or indirect influence on the formation of the crystal defects.

Controlled motion and positioning of colloids and macromolecular complexes in a fluid, as well as catalytic particles in active environments, are fundamental processes in physics, chemistry and biology. Here we focus on an active biological system for which precise experimental results are available. Our work is fully inspired by studies of one of the most widespread and ancient mechanisms of liquid phase macromolecular segregation and positioning known in nature: bacterial DNA segregation systems. Efficient bacterial chromosome segregation typically requires the coordinated action of a three-component, fueled by adenosine triphosphate machinery called the partition complex. We can distinguish two steps: (i) a process of phase transition [2,3] to built a membraneless region of high protein concentration (partition complex) (ii) the action of molecular motor action upon the complex to create a chemical force. We present a phenomenological model [1] accounting for the dynamics of this system that is also relevant for the physics of catalytic particles in active environments. The model is obtained by coupling simple linear reaction-diffusion equations with a volumetric chemophoresis force field that arises from protein-protein interactions and provides a physically viable mechanism for complex translocation. This description captures experimental observations: dynamic oscillations of complex components, complex separation and symmetrical positioning. The predictions of our model are in agreement with and provide substantial insight into recent experiments. From a non-linear physics view point, this system explores the active separation of matter at micrometric scales with a dynamical instability between static positioning and travelling wave regimes triggered by the dynamical spontaneous breaking of rotational symmetry. We also discuss the phase transition mechanism giving rise to macromolecular assembly of proteins. Our predictions are compared to Super Resolution microscopy and microbiology experiments [1,2,3].[1] Walter J.-C., Dorignac J., Lorman V., Rech J., Bouet J.-Y., Nollmann M., Palmeri J., Parmeggiani A. and Geniet F., Phys. Rev. Lett. 119, 028101 (2017).[2] Debaugny R., Sanchez A., Rech J., Labourdette D., Dorignac J., Geniet F., Palmeri J., Parmeggiani A., Boudsocq, Leberre V., Walter* J.-C. and Bouet* J.-Y Mol. Syst. Biol. 14, e8516 (2018)[3] David G., Walter J.-C., Broedersz C., Dorignac J., Geniet F., Parmeggiani A., Walliser N.-O. and Palmeri J., submitted to Phys. Rev. Lett. [arXiv/1811.09234] (2019).