On the mechanism behind the inverse melting in systems with competing interactions.

The competition between a short range attractive interaction and a nonlocal repulsive interaction promote the appearance of modulated phases. In this work we present the microscopic mechanisms leading to the emergence of inverse transitions in such systems by considering a thorough mean-field analysis of a variety of minimal models with different competing interactions. We identify the specific connections between the characteristic energy of the homogeneous and modulated phases and the observed reentrant behaviors in the phase diagram.

Nature of long-range order in stripe-forming systems with long-range repulsive interactions.

We study two dimensional stripe forming systems with competing repulsive interactions decaying as r(-α). We derive an effective Hamiltonian with a short-range part and a generalized dipolar interaction which depends on the exponent α. An approximate map of this model to a known XY model with dipolar interactions allows us to conclude that, for α<2 long-range orientational order of stripes can exist in two dimensions, and establish the universality class of the models.

Observing Pt nanoparticle formation at the atomic level during polyol synthesis.

This study investigated the synthesis of platinum nanoparticles (Pt NPs) in ethylene glycol using low cost and low toxicity chemicals as reducing (ascorbic acid) and stabilizing agents (polyvinylpyrrolidone and sodium citrate). By monitoring the changes in the local chemical environment of the Pt atoms in real time by in situ dispersive X-ray absorption spectroscopy, it is observed that the NP formation kinetics involved three different stages within 3 h 30 min of the reaction: a reduction-nucleation burst, followed by diffusion-limited Ostwald ripening growth and subsequent stabilization of the NPs. The resulting Pt NPs were analyzed by transmission electron microscopy and X-ray diffraction, revealing a monodisperse average size distribution of 2.

Spatial correlation functions and dynamical exponents in very large samples of four-dimensional spin glasses.

The study of the low temperature phase of spin glass models by means of Monte Carlo simulations is a challenging task, because of the very slow dynamics and the severe finite-size effects they show. By exploiting at the best the capabilities of standard modern CPUs (especially the streaming single instruction, multiple data extensions), we have been able to simulate the four-dimensional Edwards-Anderson model with Gaussian couplings up to sizes L=70 and for times long enough to accurately measure the asymptotic behavior. By quenching systems of different sizes to the critical temperature and to temperatures in the whole low temperature phase, we have been able to identify the regime where finite-size effects are negligible: ξ(t)≲L/7.