1,721,003 research outputs found
Phase Coexistence and Edge Currents in the Chiral Lennard-Jones Fluid
Full text linkWe study a model chiral fluid in two dimensions composed of Brownian disks interacting via a Lennard-Jones potential and a nonconservative transverse force, mimicking colloids spinning at a given rate. The system exhibits a phase separation between a chiral liquid and a dilute gas phase that can be characterized using a thermodynamic framework. We compute the equations of state and show that the surface tension controls interface corrections to the coexisting pressure predicted from the equal-area construction. Transverse forces increase surface tension and generate edge currents at the liquid-gas interface. The analysis of these currents shows that the rotational viscosity introduced in chiral hydrodynamics is consistent with microscopic bulk mechanical measurements. Chirality can also break the solid phase, giving rise to a dense fluid made of rotating hexatic patches. Our Letter paves the way for the development of the statistical mechanics of chiral particles assemblies
Noise-Induced phase separation and time reversal symmetry breaking in active field theories driven by persistent noise
No full textWithin the Landau-Ginzburg picture of phase transitions, scalar field theories develop phase separation because of a spontaneous symmetry-breaking mechanism. This picture works in thermodynamics but also in the dynamics of phase separation. Here we show that scalar nonequilibrium field theories undergo phase separation just because of nonequilibrium fluctuations driven by a persistent noise. The mechanism is similar to what happens in motility-induced phase separation where persistent motion introduces an effective attractive force. We observe that noise-induced phase separation occurs in a region of the phase diagram where disordered field configurations would otherwise be stable at equilibrium. Measuring the local entropy production rate to quantify the time-reversal symmetry breaking, we find that such breaking is concentrated on the boundary between the two phases
Dynamics of Motility-Induced clusters: coarsening beyond Ostwald ripening
Full text linkWe study the dynamics of clusters of Active Brownian Disks generated by
Motility-Induced Phase Separation, by applying an algorithm that we devised to
track cluster trajectories. We identify an aggregation mechanism that goes
beyond Ostwald ripening but also yields . Active clusters of mass
self-propel with enhanced diffusivity Pe. Their fast
motion drives aggregation into large fractal structures, which are patchworks
of diverse hexatic orders, and coexist with regular, orientationally uniform,
smaller ones. To bring out the impact of activity, we perform a comparative
study of a passive system that evidences major differences with the active
case.Comment: 6 pages, 5 figures, S
Statistical Mechanics of non−reciprocally interacting Ising spins
Full text linkTreballs Finals de Màster en Física dels Sistemes Complexos i Biofísica, Facultat de Física, Universitat de Barcelona. Curs: 2022-2023. Tutor:Demian LevisNon−reciprocal interactions are present in a large number of out−of−equilibrium systems such as active matter, social, ecological and non−Hermitian quantum systems. They are believed to be responsible for non−equilibrium phase transitions and are, still, an open topic of major interest in recent research. In this work, we present a generalization of the Ising model that includes non−reciprocal interactions among spins and analytically characterize the mean field stationary behaviour of two proposed models that incorporate non−reciprocal interactions. We show how the models exhibit a first order phase transition and how their mean field solutions are no longer spin−inversion symmetric. Furthermore, we also study d = 1 spin chains with nearest neighbours interactions, and derive the evolution equations for the first two moments. Finally, we
discuss the dynamical equations for the proposed models. The derived dynamic equations signal the presence of steady currents, e.g. traveling states, in non−reciprocally interacting spin chains
Non-reciprocal interactions in the XY Model
Full text linkTreballs Finals de Màster en Física dels Sistemes Complexos i Biofísica, Facultat de Física, Universitat de Barcelona. Curs: 2022-2023. Tutor: Demian Levis SotomayorThis work focuses on the investigation of non-reciprocal interactions in the XY Model using the Kuramoto model of synchronization in the overdamped limit. Initially, we provide partial results of the reciprocal XY Model by examining the spatial correlation function and the transition temperature. Through a comparison of simulation and theoretical results, we gain insights into the critical behavior of the model. To extend the analysis, we introduce non-reciprocal interactions using the Kuramoto model in the overdamped regime, which offers a nonlinear mathematical framework for understanding the dynamics of the system. This is particularly relevant as the reciprocal XY Model lacks a Hamiltonian description. By incorporating non-reciprocal interactions, we observe that the system does not undergo a topological phase transition. Instead, a dynamic analysis
reveals, under certain initial distribution and conditions, the emergence of waves and their characteristic
propagation. We explore these phenomena in both one-dimensional and two-dimensional scenarios, demonstrating that the waves propagate with a linear velocity and exhibit a linear dispersion relatio
Motility-Induced Phase Separation of harmonic Active Ornstein-Uhlenbeck particles fulfilling Detailed Balance
Full text linkTreballs Finals de Màster en Física dels Sistemes Complexos i Biofísica, Facultat de Física, Universitat de Barcelona. Curs: 2021-2022. Tutor: Demian LevisActive matter constitutes a class of nonequilibrium systems which has attracted a lot of attention over the past decades, and Motility-Induced Phase Separation (MIPS) lies among one of its most salient collective phenomena. Although MIPS has been studied in depth, the question of whether this active phase transition can only occur in the presence of out-of-equilibrium fluctuations remains open. In this work, we numerically show that harmonic Active Ornstein-Uhlenbeck Particles (AOUP), with an equilibrium dynamics fulfilling detailed balance, undergo MIPS. We studied analytically 2-body interactions, identifying an effective attraction increasing with activity, to show that n-body effects are needed in order to account for the nature of the transition, and in particular, of the dense phase. Finally, a recursive method to obtain a multibody
expansion of the partition function for the complete system is develope
Dynamical mean-field theory for non-reciprocal spin-glasses
No full textTreballs Finals de Màster en Física dels Sistemes Complexos i Biofísica, Facultat de Física, Universitat de Barcelona. Curs: 2023-2024. Tutor: Demian LevisIn out-of-equilibrium systems, the lack of reciprocity in interactions is more the rule than the exception. Non-reciprocal interactions arise generically in out-of-equilibrium systems, such as metamaterials, neural networks, or ecosystems. In the context of glassy systems, it is known that they are crucial in the process of learning in neural networks but their role in glassy dynamics is still widely debated. In this work, we develop a generalization of a dynamical mean-field theory of spinglass models which includes non-reciprocal interactions among spins, with full analytical detail.
Furthermore, we show how the dynamics of mean-field spin-glasses are quantitatively and qualitatively modified when considering non-reciprocal interactions, focusing on the high-temperature relaxational dynamics. Our theory predicts critical slowing down of the dynamics and glass melting when considering weakly non-reciprocal interactions, although we suspect that new physics can be further explored beyond that limi
Dynamical mean-field theory for non-reciprocal spin-glasses
Full text linkTreballs Finals de Màster en Física dels Sistemes Complexos i Biofísica, Facultat de Física, Universitat de Barcelona. Curs: 2023-2024. Tutor: Demian LevisIn out-of-equilibrium systems, the lack of reciprocity in interactions is more the rule than the exception. Non-reciprocal interactions arise generically in out-of-equilibrium systems, such as metamaterials, neural networks, or ecosystems. In the context of glassy systems, it is known that they are crucial in the process of learning in neural networks but their role in glassy dynamics is still widely debated. In this work, we develop a generalization of a dynamical mean-field theory of spinglass models which includes non-reciprocal interactions among spins, with full analytical detail.
Furthermore, we show how the dynamics of mean-field spin-glasses are quantitatively and qualitatively modified when considering non-reciprocal interactions, focusing on the high-temperature relaxational dynamics. Our theory predicts critical slowing down of the dynamics and glass melting when considering weakly non-reciprocal interactions, although we suspect that new physics can be further explored beyond that limi
Collective and emergent dynamics in active systems
No full textTreballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2016, Tutors: Ignacio Pagonabarraga, Demian LevisWe study some non-equilibrium properties of active matter, such as self-propulsion, that causes the emergence of phenomena not observed in equilibrium systems. By applying the UCNA approximation we are able to derive a probability density function under stationary conditions that enables us to study the behaviour of active particles in the presence of a perturbation such as a hard wall modelled by a repulsive potential. From here, we calculate the adsorption near the wall and we study the dependence it has on activity. We find that adsorption grows approximately as the square root of the activity, regardless if the potential is strictly repulsive or repulsive and attractive in different regions of spac
- …
