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Ref Arxiv: 1606.03108
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DOI: 10.1103/PhysRevE.95.012112
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Ising spin-glass models with bimodal, Gaussian, uniform, and Laplacian interaction distributions in dimension five are studied through detailed numerical simulations. The data are analyzed in both the finite-size scaling regime and the thermodynamic limit regime. It is shown that the values of critical exponents and of dimensionless observables at criticality are model dependent. Models in a single universality class have identical values for each of these critical parameters, so Ising spin-glass models in dimension five with different interaction distributions each lie in different universality classes. This result confirms conclusions drawn from measurements in dimension four and dimension two.

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DOI: 10.1088/1742-5468/aa4e92
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DOI: 10.1103/PhysRevA.95.012138
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We investigate the transport of energy in a linear chain of two-level quantum emitters (atoms) weakly coupled to a blackbody radiation bath. We show that simply by displacing one or more atoms from their regular-chain positions, the efficiency of the energy transport can be considerably amplified of at least one order of magnitude. In addition, in configurations providing an efficiency greater than 100%, the distance between the last two atoms of the chain can be up to 20 times larger than the one in the regular chain, thus achieving a much longer-range energy transport. By performing both a stationary and time-dependent analysis, we ascribe this effect to an elementary block of three atoms, playing the role of excitation injector from the blackbody bath to the extraction site. By considering chains with up to seven atoms, we also show that the amplification is robust and can be further enhanced up to 1400%.

Commentaires: Article 012138

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I'll discuss the modular properties of D3-brane instantons appearing in Calabi-Yau string compactifications. I'll show that the D3-instanton contribution to a certain geometric potential on the hypermultiplet moduli space can be related to the elliptic genus of (0,4) SCFT. The modular properties of the potential imply that the elliptic genus associated with non-primitive divisors of Calabi-Yau is only mock modular. I'll show how to construct its modular completion and to make manifest the modular invariance of the twistorial construction of D-instanton corrected hypermultiplet moduli space.

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Computer simulations give precious insight into the microscopic behavior of amorphous materials, but their typical timescales are orders of magnitude shorter than the experimentally relevant ones. We close this enormous gap for a class of polydisperse models, which we successfully equilibrate beyond experimental timescales by means of the swap Monte Carlo algorithm. This numerical advance allows us to address some crucial outstanding questions, such as the relationship between jamming and glass transitions and the relevance of an entropy crisis for glass formation.

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Ref Arxiv: 1609.07979
DOI: 10.1063/1.4972525
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Classical particle systems characterized by continuous size polydispersity, such as colloidal materials, are not straightforwardly described using statistical mechanics, since fundamental issues may arise from particle distinguishability. Because the mixing entropy in such systems is divergent in the thermodynamic limit we show that the configurational entropy estimated from standard computational approaches to characterize glassy states also diverges. This reasoning would suggest that polydisperse materials cannot undergo a glass transition, in contradiction to experiments. We explain that this argument stems from the confusion between configurations in phase space and states defined by free energy minima, and propose a simple method to compute a finite and physically meaningful configurational entropy in continuously polydisperse systems. Physically, the proposed approach relies on an effective description of the system as an $M^*$-component system with a finite $M^*$, for which finite mixing and configurational entropies are obtained. We show how to directly determine $M^*$ from computer simulations in a range of glass-forming models with different size polydispersities, characterized by hard and soft interparticle interactions, and by additive and non-additive interactions. Our approach provides consistent results in all cases and demonstrates that the configurational entropy of polydisperse system exists, is finite, and can be quantitatively estimated.

Commentaires: 13 pages, 4 figures. v2: Published version. Réf Journal: J. Chem. Phys. 146, 014502 (2017)

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DOI: 10.1007/978-3-319-65436-2
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Dynamic Nuclear Polarization and Nuclear Fields