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See detailThermodynamics of Active Field Theories: Energetic Cost of Coupling to Reservoirs
Markovich, Tomer; Fodor, Etienne UL; Tjhung, Elsen et al

in PHYSICAL REVIEW X (2021), 11(2),

The hallmark of active matter is the autonomous directed motion of its microscopic constituents driven by consumption of energy resources. This motion leads to the emergence of large-scale dynamics and ... [more ▼]

The hallmark of active matter is the autonomous directed motion of its microscopic constituents driven by consumption of energy resources. This motion leads to the emergence of large-scale dynamics and structures without any equilibrium equivalent. Though active field theories offer a useful hydrodynamic description, it is unclear how to properly quantify the energetic cost of the dynamics from such a coarse-grained description. We provide a thermodynamically consistent framework to identify the energy exchanges between active systems and their surrounding thermostat at the hydrodynamic level. Based on linear irreversible thermodynamics, we determine how active fields couple with the underlying reservoirs at the basis of nonequilibrium driving. This approach leads to evaluating the rate of heat dissipated in the thermostat, as a measure of the cost to sustain the system away from equilibrium, which is related to the irreversibility of the active field dynamics. We demonstrate the applicability of our approach in two popular active field theories: (i) the dynamics of a conserved density field reproducing active phase separation and (ii) the coupled dynamics of density and polarization describing motile deformable droplets. Combining numerical and analytical approaches, we provide spatial maps of dissipated heat, compare them with the irreversibility measure of the active field dynamics, and explore how the overall dissipated heat varies with the emerging order. [less ▲]

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See detailStochastic and Quantum Thermodynamics of Driven RLC Networks
Freitas, Jose Nahuel UL; Delvenne, Jean-Charles; Esposito, Massimiliano UL

in Physical Review X (2020)

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See detailField Dependence of Magnetic Disorder in Nanoparticles
Zákutná, Dominika; Nižňanský, Daniel; Barnsley, Lester C. et al

in Physical Review X (2020), 10

The performance characteristics of magnetic nanoparticles toward application, e.g., in medicine and imaging or as sensors, are directly determined by their magnetization relaxation and total magnetic ... [more ▼]

The performance characteristics of magnetic nanoparticles toward application, e.g., in medicine and imaging or as sensors, are directly determined by their magnetization relaxation and total magnetic moment. In the commonly assumed picture, nanoparticles have a constant overall magnetic moment originating from the magnetization of the single-domain particle core surrounded by a surface region hosting spin disorder. In contrast, this work demonstrates the significant increase of the magnetic moment of ferrite nanoparticles with an applied magnetic field. At low magnetic field, the homogeneously magnetized particle core initially coincides in size with the structurally coherent grain of 12.8(2) nm diameter, indicating a strong coupling between magnetic and structural disorder. Applied magnetic fields gradually polarize the uncorrelated, disordered surface spins, resulting in a magnetic volume more than 20% larger than the structurally coherent core. The intraparticle magnetic disorder energy increases sharply toward the defect-rich surface as established by the field dependence of the magnetization distribution. In consequence, these findings illustrate how the nanoparticle magnetization overcomes structural surface disorder. This new concept of intraparticle magnetization is deployable to other magnetic nanoparticle systems, where the in-depth knowledge of spin disorder and associated magnetic anisotropies are decisive for a rational nanomaterials design. [less ▲]

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See detailHow Dissipation Constrains Fluctuations in Nonequilibrium Liquids: Diffusion, Structure, and Biased Interactions
Tociu, Laura; Fodor, Etienne UL; Nemoto, Takahiro et al

in PHYSICAL REVIEW X (2019), 9(4),

The dynamics and structure of nonequilibrium liquids, driven by nonconservative forces which can be either external or internal generically hold the signature of the net dissipation of energy in the ... [more ▼]

The dynamics and structure of nonequilibrium liquids, driven by nonconservative forces which can be either external or internal generically hold the signature of the net dissipation of energy in the thermostat. Yet, disentangling precisely how dissipation changes collective effects remains challenging in many-body systems due to the complex interplay between driving and particle interactions. First, we combine explicit coarse-graining and stochastic calculus to obtain simple relations between diffusion, density correlations, and dissipation in nonequilibrium liquids. Based on these results, we consider large-deviation biased ensembles where trajectories mimic the effect of an external drive. The choice of the biasing function is informed by the connection between dissipation and structure derived in the first part. Using analytical and computational techniques, we show that biasing trajectories effectively renormalizes interactions in a controlled manner, thus providing intuition on how driving forces can lead to spatial organization and collective dynamics. Altogether, our results show how tuning dissipation provides a route to alter the structure and dynamics of liquids and soft materials. [less ▲]

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See detailAutonomous Engines Driven by Active Matter: Energetics and Design Principles
Pietzonka, Patrick; Fodor, Etienne UL; Lohrmann, Christoph et al

in PHYSICAL REVIEW X (2019), 9(4),

Because of its nonequilibrium character, active matter in a steady state can drive engines that autonomously deliver work against a constant mechanical force or torque. As a generic model for such an ... [more ▼]

Because of its nonequilibrium character, active matter in a steady state can drive engines that autonomously deliver work against a constant mechanical force or torque. As a generic model for such an engine, we consider systems that contain one or several active components and a single passive one that is asymmetric in its geometrical shape or its interactions. Generally, one expects that such an asymmetry leads to a persistent, directed current in the passive component, which can be used for the extraction of work. We validate this expectation for a minimal model consisting of an active and a passive particle on a one-dimensional lattice. It leads us to identify thermodynamically consistent measures for the efficiency of the conversion of isotropic activity to directed work. For systems with continuous degrees of freedom, work cannot be extracted using a one-dimensional geometry under quite general conditions. In contrast, we put forward two-dimensional shapes of a movable passive obstacle that are best suited for the extraction of work, which we compare with analytical results for an idealized work-extraction mechanism. For a setting with many noninteracting active particles, we use a mean-field approach to calculate the power and the efficiency, which we validate by simulations. Surprisingly, this approach reveals that the interaction with the passive obstacle can mediate cooperativity between otherwise noninteracting active particles, which enhances the extracted power per active particle significantly. [less ▲]

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See detailQuantum and Information Thermodynamics: A Unifying Framework Based on Repeated Interactions
Strasberg, Philipp UL; Schaller, Gernot; Brandes, Tobias et al

in Physical Review X (2017), 7(021003),

We expand the standard thermodynamic framework of a system coupled to a thermal reservoir by <br />considering a stream of independently prepared units repeatedly put into contact with the system. These ... [more ▼]

We expand the standard thermodynamic framework of a system coupled to a thermal reservoir by <br />considering a stream of independently prepared units repeatedly put into contact with the system. These <br />units can be in any nonequilibrium state and interact with the system with an arbitrary strength and <br />duration. We show that this stream constitutes an effective resource of nonequilibrium free energy, and we <br />identify the conditions under which it behaves as a heat, work, or information reservoir. We also show that <br />this setup provides a natural framework to analyze information erasure (“Landauer’s principle”) and <br />feedback-controlled systems (“Maxwell’s demon”). In the limit of a short system-unit interaction time, we <br />further demonstrate that this setup can be used to provide a thermodynamically sound interpretation to <br />many effective master equations. We discuss how nonautonomously driven systems, micromasers, lasing <br />without inversion and the electronic Maxwell demon can be thermodynamically analyzed within our <br />framework. While the present framework accounts for quantum features (e.g., squeezing, entanglement, <br />coherence), we also show that quantum resources do not offer any advantage compared to classical ones in <br />terms of the maximum extractable work. [less ▲]

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See detailEntropy Production in Field Theories without Time-Reversal Symmetry: Quantifying the Non-Equilibrium Character of Active Matter
Nardini, Cesare; Fodor, Etienne UL; Tjhung, Elsen et al

in PHYSICAL REVIEW X (2017), 7(2),

Active-matter systems operate far from equilibrium because of the continuous energy injection at the scale of constituent particles. At larger scales, described by coarse-grained models, the global ... [more ▼]

Active-matter systems operate far from equilibrium because of the continuous energy injection at the scale of constituent particles. At larger scales, described by coarse-grained models, the global entropy production rate S quantifies the probability ratio of forward and reversed dynamics and hence the importance of irreversibility at such scales: It vanishes whenever the coarse-grained dynamics of the active system reduces to that of an effective equilibrium model. We evaluate S for a class of scalar stochastic field theories describing the coarse-grained density of self-propelled particles without alignment interactions, capturing such key phenomena as motility-induced phase separation. We show how the entropy production can be decomposed locally (in real space) or spectrally (in Fourier space), allowing detailed examination of the spatial structure and correlations that underly departures from equilibrium. For phase-separated systems, the local entropy production is concentrated mainly on interfaces, with a bulk contribution that tends to zero in the weak-noise limit. In homogeneous states, we find a generalized Harada-Sasa relation that directly expresses the entropy production in terms of the wave-vector-dependent deviation from the fluctuation-dissipation relation between response functions and correlators. We discuss extensions to the case where the particle density is coupled to a momentum-conserving solvent and to situations where the particle current, rather than the density, should be chosen as the dynamical field. We expect the new conceptual tools developed here to be broadly useful in the context of active matter allowing one to distinguish when and where activity plays an essential role in the dynamics. [less ▲]

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See detailNonequilibrium Thermodynamics of Chemical Reaction Networks: Wisdom from Stochastic Thermodynamics
Rao, Riccardo UL; Esposito, Massimiliano UL

in Physical Review X (2016), 6(4), 041064

We build a rigorous nonequilibrium thermodynamic description for open chemical reaction networks of <br /><br />elementary reactions. Their dynamics is described by deterministic rate equations with mass ... [more ▼]

We build a rigorous nonequilibrium thermodynamic description for open chemical reaction networks of <br /><br />elementary reactions. Their dynamics is described by deterministic rate equations with mass action <br /><br />kinetics. Our most general framework considers open networks driven by time-dependent chemostats. <br /><br />The energy and entropy balances are established and a nonequilibrium Gibbs free energy is introduced. <br /><br />The difference between this latter and its equilibrium form represents the minimal work done by the <br /><br />chemostats to bring the network to its nonequilibrium state. It is minimized in nondriven detailed-balanced <br /><br />networks (i.e., networks that relax to equilibrium states) and has an interesting information-theoretic <br /><br />interpretation. We further show that the entropy production of complex-balanced networks (i.e., networks <br /><br />that relax to special kinds of nonequilibrium steady states) splits into two non-negative contributions: one <br /><br />characterizing the dissipation of the nonequilibrium steady state and the other the transients due to <br /><br />relaxation and driving. Our theory lays the path to study time-dependent energy and information <br /><br />transduction in biochemical networks. [less ▲]

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See detailThermodynamics with Continuous Information Flow
Horowitz, Jordan M.; Esposito, Massimiliano UL

in Physical Review X (2014), 4

as nonautonomous systems described by stochastic thermodynamics. We demonstrate how information is <br />continuously generated in an auxiliary system and then transferred to a relevant system that can ... [more ▼]

as nonautonomous systems described by stochastic thermodynamics. We demonstrate how information is <br />continuously generated in an auxiliary system and then transferred to a relevant system that can utilize it to <br />fuel otherwise impossible processes. Indeed, while the joint system satisfies the second law, the entropy <br />balance for the relevant system is modified by an information term related to the mutual information rate <br />between the two systems. We show that many important results previously derived for nonautonomous <br />Maxwell demons can be recovered from our formalism and use a cycle decomposition to analyze the <br />continuous information flow in autonomous systems operating at a steady state. A model system is used to <br />illustrate our findings. [less ▲]

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See detailDirac Cones, Topological Edge States, and Nontrivial Flat Bands in Two-Dimensional Semiconductors with a Honeycomb Nanogeometry
Kalesaki, Efterpi UL; Delerue, Christophe; Morais Smith, Cristiane et al

in Physical Review X (2014), 4(1), 011010

We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties ... [more ▼]

We study theoretically two-dimensional single-crystalline sheets of semiconductors that form a honeycomb lattice with a period below 10 nm. These systems could combine the usual semiconductor properties with Dirac bands. Using atomistic tight-binding calculations, we show that both the atomic lattice and the overall geometry influence the band structure, revealing materials with unusual electronic properties. In rocksalt Pb chalcogenides, the expected Dirac-type features are clouded by a complex band structure. However, in the case of zinc-blende Cd-chalcogenide semiconductors, the honeycomb nanogeometry leads to rich band structures, including, in the conduction band, Dirac cones at two distinct energies and nontrivial flat bands and, in the valence band, topological edge states. These edge states are present in several electronic gaps opened in the valence band by the spin-orbit coupling and the quantum confinement in the honeycomb geometry. The lowest Dirac conduction band has S-orbital character and is equivalent to the π−π⋆ band of graphene but with renormalized couplings. The conduction bands higher in energy have no counterpart in graphene; they combine a Dirac cone and flat bands because of their P-orbital character. We show that the width of the Dirac bands varies between tens and hundreds of meV. These systems emerge as remarkable platforms for studying complex electronic phases starting from conventional semiconductors. Recent advancements in colloidal chemistry indicate that these materials can be synthesized from semiconductor nanocrystals. [less ▲]

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