Latest Research Papers In Condensed Matter Physics | (Cond-Mat.Stat-Mech) 2019-07-02
Statistical Mechanics
Generalized criteria of symmetry breaking. A strategy for quantum time crystals (1906.12293v1)
Carlo Heissenberg, Franco Strocchi
2019-06-28
The aim of this paper is to propose a criterion of spontaneous symmetry breaking that makes reference to the properties of pure phases defined by a translationally invariant state. By avoiding any reference to the ground state, at the basis of the standard approach, this criterion applies to a wider class of models. An interesting application is the breaking of time translations. Indeed, we discuss explicit theoretical models which exhibit the prototypical features of quantum time crystals, without the need of a time-dependent Hamiltonian.
Robustness of delocalization to the inclusion of soft constraints in long-range random models (1904.11509v2)
P. A. Nosov, I. M. Khaymovich
2019-04-25
Motivated by the constrained many-body dynamics, the stability of the localization-delocalization properties to the inclusion of the soft constraints is addressed in random matrix models. These constraints are modeled by correlations in long-ranged hopping with Pearson correlation coefficient different from zero or unity. Counterintuitive robustness of delocalized phases, both ergodic and (multi)fractal, in these models is numerically observed and confirmed by the analytical calculations. First, matrix inversion trick is used to uncover the origin of such robustness. Next, to characterize delocalized phases a method of eigenstate calculation, sensitive to correlations in long-ranged hopping terms, is developed for random matrix models and approved by numerical calculations and previous analytical ansatz. The effect of the robustness of states in the bulk of the spectrum the inclusion of to soft constraints is generally discussed for single-particle and many-body systems.
Skyrmion relaxation dynamics in the presence of quenched disorder (1906.12146v1)
Barton L. Brown, Uwe C. Täuber, Michel Pleimling
2019-06-28
Using Langevin molecular dynamics simulations we study relaxation processes of interacting skyrmion systems with and without quenched disorder. Using the typical diffusion length as the time-dependent length characterizing the relaxation process, we find that clean systems always display dynamical scaling, and this even in cases where the typical length is not a simple power law of time. In the presence of the Magnus force, two different regimes are identified as a function of the noise strength. The Magnus force has also a major impact when attractive pinning sites are present, as this velocity-dependent force helps skyrmions to bend around defects and avoid caging effects. With the exception of the limit of large noise, for which dynamical scaling persists even in the presence of quenched disorder, attractive pinning sites capture a substantial fraction of skyrmions which results in a complex behavior of the two-time auto-correlation function that is not reproduced by a simple aging scaling ansatz.
Determining Free Energy Differences Through Variational Morphing (1906.12124v1)
Martin Reinhardt, Helmut Grubmüller
2019-06-28
Free energy calculations based on atomistic Hamiltonians and sampling are key to a first principles understanding of biomolecular processes, material properties, and macromolecular chemistry. Here, we generalize the Free Energy Perturbation method and derive non-linear Hamiltonian transformation sequences for optimal sampling accuracy that differ markedly from established linear transformations. We show that our sequences are also optimal for the Bennett Acceptance Ratio (BAR) method, and our unifying framework generalizes BAR to small sampling sizes and non-Gaussian error distributions. Simulations on a Lennard-Jones gas show that an order of magnitude less sampling is required compared to established methods.
Diffusion-controlled reactions on non-spherical partially absorbing axisymmetric surfaces (1906.12105v1)
Francesco Piazza, Denis Grebenkov
2019-06-28
The calculation of the diffusion-controlled reaction rate for partially absorbing, non-spherical boundaries presents a formidable problem of broad relevance. In this paper we take the reference case of a spherical boundary and work out a perturbative approach to get a simple analytical formula for the first-order correction to the diffusive flux onto a non-spherical partially absorbing surface of revolution. To assess the range of validity of this formula, we also derive exact and approximate expressions for the reaction rate in the case of partially absorbing prolate and oblate spheroids. Our solution provides a handy way to assess the effect of non-sphericity on the rate of capture in the general case of partial surface reactivity.
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