Ref HAL: hal-01631144_v1
DOI: 10.1063/1.4997124
WoS: WOS:000412074000003
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6 Citations
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III-nitride-on-silicon L3 and H2 photonic crystal cavities with resonances down to 315 nm and quality factors up to 1085 at 337 nm have been demonstrated. The reduction of quality factor (Q) with decreasing wavelength is investigated. Besides the QW absorption below 340 nm a noteworthy contribution is attributed to the residual absorption present in thin AlN layers grown on silicon, as measured by spectroscopic ellipsometry. This residual absorption ultimately limits the Q factor to around 250 at 300 nm when no active layer is present.

Ref HAL: hal-01631138_v1
DOI: 10.1103/PhysRevLett.119.113902
WoS: WOS:000410897100007
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18 Citations
Résumé:

The spontaneous emergence of vector vortex beams with non-uniform polarization distribution is reported in a vertical-cavity surface-emitting laser with frequency-selective feedback. Anti-vortices with a hyperbolic polarization structure and radially polarized vortices are demonstrated. They exist close to and partially coexist with vortices with uniform and non-uniform polarization distributions characterized by four domains of pairwise orthogonal polarization. These vector vortices are argued to have soliton-like properties. Independently of this interpretation, the novel way of generating these nontrivial structures in a remarkably simple VCSEL system is regarded to be interesting and potentially beneficial for other experiments utilizing non-uniform polarization structures.

Ref HAL: hal-01630755_v1
Ref Arxiv: 1704.08257
DOI: 10.1073/pnas.1706860114
WoS: 000413520700049
Ref. & Cit.: NASA ADS
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47 Citations
Résumé:

Liquids relax extremely slowly upon approaching the glass state. One explanation is that an entropy crisis, due to the rarefaction of available states, makes it increasingly arduous to reach equilibrium in that regime. Validating this scenario is challenging, because experiments offer limited resolution, while numerical studies lag more than eight orders of magnitude behind experimentally-relevant timescales. In this work we not only close the colossal gap between experiments and simulations but manage to create in-silico configurations that have no experimental analog yet. Deploying a range of computational tools, we obtain four estimates of their configurational entropy. These measurements consistently confirm that the steep entropy decrease observed in experiments is also found in simulations, even beyond the experimental glass transition. Our numerical results thus extend the new observational window into the physics of glasses and reinforce the relevance of an entropy crisis for understanding their formation.

Commentaires: 4+23 pages, 3+12 figures; v2: final version, with various changes made. Data relevant to this work can be accessed at http://dx.doi.org/10.7924/G8ZG6Q9T. Réf Journal: PNAS 114, 11356-11361 (2017)

Ref HAL: hal-01629354_v1
Ref Arxiv: 1706.02528
Ref. & Cit.: NASA ADS
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We develop a method of non-perturbative optical control over adiabatic remagnetisation of the nuclear spin system and apply it to verify the spin temperature concept in GaAs microcavities. The nuclear spin system is shown to exactly follow the predictions of the spin-temperature theory, despite the quadrupole interaction that was earlier reported to disrupt nuclear spin thermalisation. These findings open a way to deep cooling of nuclear spins in semiconductor structures, with a prospect of realisation of nuclear spin-ordered statesfor high fidelity spin-photon interfaces.

Commentaires: 7 pages, 4 figures

Ref HAL: hal-01628314_v1
DOI: 10.1016/j.bbagen.2017.10.013
WoS: 000425197300034
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2 Citations
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Metastasis formation is a complex and not entirely understood process. The poorest prognosis and the most feared complications are associated to brain metastases. Melanoma derived brain metastases show the highest prevalence. Due to the lack of classical lymphatic drainage, in the process of brain metastases formation the haematogenous route is of primordial importance. The first and crucial step in this multistep process is the establishment of firm adhesion between the blood travelling melanoma cells and the tightly connected layer of the endothelium, which is the fundamental structure of the blood-brain barrier. This study compares the de-adhesion properties and dynamics of three melanoma cells types (WM35, A2058 and A375) to a confluent layer of brain micro-capillary endothelial cells. Cell type dependent adhesion characteristics are presented, pointing towards the existence of metastatic potential related nanomechanical aspects. Apparent mechanical properties such as elasticity, maximal adhesion force, number, size and distance of individual rupture events showed altered values pointing towards cell type dependent aspects. Our results underline the importance of mechanical details in case of intercellular interactions. Nevertheless, it suggests that in adequate circumstances elastic and adhesive characterizations might be used as biomarkers.

Ref HAL: hal-01627920_v1
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Active motion of living or artificial systems (active colloids) may occur in strong confinement or in complex environments such membranes. In confinement, the propulsion mechanism and motion features may strongly differ from the ones observed in the bulk of a simple fluid. As a primary form of confinement, we consider a single interface. Recently, we show that the interface between a liquid and a fluid dramatically affects the lateral frictions of partially wetted colloidal particles [1]. In this contribution, the impact of partial wetting dynamics on the motion of active Janus colloids will be presented. Spherical catalytic Janus colloids have been prepared by coating half surface of silica particles with a thin platinum layer. Immersion depth of the Janus colloids as well as their orientation with respect to the water surface reveal complex and rich wetting properties of Janus particles at the liquid-gas interface [2]. Active motion of Janus colloids at the interface in the presence of various concentrations of hydrogen peroxide, H2O2, has been studied. The types of observed trajectories, directional and circular ones, revealed the effective force and torque induced by the catalytic decomposition of H2O2 fuel. At the water surface, the persistence of directional active motion is greatly enhanced when compared to the motion in bulk [3]. This result has been explained in terms of loss of one rotational degree of freedom at the interface and also to a new contribution to the rotational friction due to partial wetting [1].[1] G. Boniello, C. Blanc, D. Fedorenko, M. Medfai, NB. Mbarek, M. In, M. Gross, A. Stocco, M. Nobili, Nature Materials 14, 908 (2015).[2] X. Wang, M. In, C. Blanc, P. Malgaretti, M. Nobili, A. Stocco, Faraday Discussions 191, 305 (2016).[3] X. Wang, M. In, C. Blanc, M. Nobili, A. Stocco, Soft Matter 11, 7376 (2015).