Gallium arsenate (GaAsO4) has the highest piezoelectric properties among α-quartz-type materials. We describe first-principles calculations of the linear and second-order nonlinear optical properties of GaAsO4 combined with measurements of its second harmonic generation (SHG). Our calculations show that GaAsO4 has a SHG efficiency between 7.1 (LDA) and 12.3 pm/V (GGA), which is in agreement with our experiments (7.5 ± 1.5 pm/V) using the technique of Maker fringes. This SHG efficiency, attributed to an electronic transition from O 2p to As 4 s states, is higher than that observed in GaPO4 due to a better polarizability of As atoms. Thus, the thermal stability of GaAsO4 (no phase transition up to its thermal decomposition at 1303 K) associated with its high laser damage threshold (0.93 GW/cm2) make this compound a promising bifunctional material for piezoelectric and nonlinear optical applications at high temperatures.

Producing wheat gluten gels with tunable mechanical properties via simple sol-gel routes would facilitate their processing into plant protein-rich food products. However, a standard gluten is a very elastic mass with a high concentration of proteins in water and is hardly processable except using high shear harsh extrusions. The wheat proteins, which are responsible for the viscoelastic properties of gluten, are among the most complex proteins families, with extremely broad polymorphisms and polydispersities, and are moreover insoluble in water, rendering rational studies difficult. We use here a novel extraction protocol that allows the formulation of stable ethanolic suspensions of gluten proteins over a wide range of concentrations. Viscoelasticity measurements show a spontaneous and concentration-dependent gelation of the suspensions, which we find to be driven by the slow formation of hydrogen bonds. We successfully rationalize our data using percolation models and relate the viscoelasticity of the gels to their fractal dimension measured by scattering techniques. The novel gluten gels display self-healing properties and their elastic plateaus covers several decades. In particular very soft gels suitable for processing can be produced.

We study an ensemble of two-level quantum systems (qubits) interacting with a common electromagnetic fieldin the proximity of a dielectric slab whose temperature is held different from that of some far surrounding walls.We show that the dissipative dynamics of the qubits driven by this stationary and out of thermal equilibriumfield allows the production of steady many-body entangled states, different from the case at thermal equilibriumwhere steady states are always nonentangled. By studying up to ten qubits, we point out the role of symmetry inthe entanglement production, which is exalted in the case of permutationally invariant configurations. In the caseof three qubits, we find a strong dependence of tripartite entanglement on the spatial disposition of the qubits,and in the case of six qubits we find several highly entangled bipartitions where entanglement can, remarkably,survive for large qubit-qubit distances up to 100 μm.

We present a descriptive review of physical problems dealing with extreme values in several fields of physics. We consider different physical situations involving random variables that are correlated or not, and study the statistics of extremal variables, which is relevant for situations where height fluctuations, catastrophic events such as material failure, or power outrage occur. We describe the general theory and relate the cumulative limit distributions that can be accessible in experiments to microscopic models. In many cases however, the random variables are correlated, in interface problems for example, and the characteristics of the interaction are revealed in the asymptotic behavior of the limit distribution.

The emergence of particle irreversibility in periodically driven colloidal suspensions has been interpreted as resulting either from a nonequilibrium phase transition to an absorbing state or from the chaotic nature of particle trajectories. Using a simple model of a driven suspension we show that a nonequilibrium phase transition is accompanied by hyperuniform static density fluctuations in the vicinity of the transition, where we also observe strong dynamic heterogeneities reminiscent of dynamics in glassy materials. We find that single particle dynamics becomes intermittent and strongly non-Fickian, and that collective dynamics becomes spatially correlated over diverging lengthscales. Our results suggest that the two theoretical scenarii can be experimentally discriminated using particle-resolved measurements of standard static and dynamic observables.

We use ab initio simulations to investigate the properties of a sodium borosilicate glass of composition 3Na2 O-B2 O3 -6SiO2 . We find that the broadening of the first peak in the radial distribution functions gBO (r) and gBNa (r) is due to the presence of trigonal and tetrahedral boron units as well as to nonbridging oxygen atoms connected to BO3 units. In agreement with experimental results, we find that the [3] B units involve a significant number of nonbridging oxygens, whereas the vast majority of [4] B have only bridging oxygens. We determine the three-dimensional distribution of the Na atoms around the [3] B and [4] B units and use this information to explain why the sodium atoms associated with the latter share more oxygen atoms with the central boron atoms than the former units. From the distribution of the electrons we calculate the total electronic density of states, as well its decomposition into angular momentum contributions. The vibrational density of states shows at high frequencies a band that originates from the motion of the boron atoms. We find that the [3] B and [4] B units give rise to well-defined features in the spectrum, which thus can be used to estimate the concentration of these structural entities. The contribution of [3] B can be decomposed further into symmetric and asymmetric parts that can also be easily identified in the spectrum. Furthermore, it is found that certain features in the spectrum can be used to obtain information on the type of atom that is the second-nearest neighbor of a boron in the [4] B unit. We calculate the average Born charges on the bridging and nonbridging oxygen atoms and show that these depend linearly on the angle between the two bonds and the distance from the connected cation, respectively. Finally, we have determined the frequency dependence of the dielectric function, as well as the absorption spectra. The latter is in good quantitative agreement with the experimental data.