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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 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 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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