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Exciton-Phonon Coupling in the Ultraviolet Absorption and Emission Spectra of Bulk Hexagonal Boron Nitride Paleari, Fulvio ; ; et al in PHYSICAL REVIEW LETTERS (2019), 122(18), 187401-6 We present an ab initio method to calculate phonon-assisted absorption and emission spectra in the presence of strong excitonic effects. We apply the method to bulk hexagonal BN, which has an indirect ... [more ▼] We present an ab initio method to calculate phonon-assisted absorption and emission spectra in the presence of strong excitonic effects. We apply the method to bulk hexagonal BN, which has an indirect band gap and is known for its strong luminescence in the UV range. We first analyze the excitons at the wave vector (q) over bar of the indirect gap. The coupling of these excitons with the various phonon modes at (q) over bar is expressed in terms of a product of the mean square displacement of the atoms and the second derivative of the optical response function with respect to atomic displacement along the phonon eigenvectors. The derivatives are calculated numerically with a finite difference scheme in a supercell commensurate with (q) over bar. We use detailed balance arguments to obtain the intensity ratio between emission and absorption processes. Our results explain recent luminescence experiments and reveal the exciton-phonon coupling channels responsible for the emission lines. [less ▲] Detailed reference viewed: 177 (8 UL)Photoinduced Phase Transitions in Ferroelectrics ; Torun, Engin ; Wirtz, Ludger et al in PHYSICAL REVIEW LETTERS (2019), 123(8), 087601-6 Ferroic materials naturally exhibit a rich number of functionalities, which often arise from thermally, chemically, or mechanically induced symmetry breakings or phase transitions. Based on density ... [more ▼] Ferroic materials naturally exhibit a rich number of functionalities, which often arise from thermally, chemically, or mechanically induced symmetry breakings or phase transitions. Based on density functional calculations, we demonstrate here that light can drive phase transitions as well in ferroelectric materials such as the perovskite oxides lead titanate and barium titanate. Phonon analysis and total energy calculations reveal that the polarization tends to vanish under illumination, to favor the emergence of nonpolar phases, potentially antiferroelectric, and exhibiting a tilt of the oxygen octahedra. Strategies to tailor photoinduced phases based on phonon instabilities in the electronic ground state are also discussed. [less ▲] Detailed reference viewed: 132 (9 UL)Extreme Decoherence and Quantum Chaos ; ; Chenu, Aurélia et al in Physical Review Letters (2019), 122 We study the ultimate limits to the decoherence rate associated with dephasing processes. Fluctuating chaotic quantum systems are shown to exhibit extreme decoherence, with a rate that scales ... [more ▼] We study the ultimate limits to the decoherence rate associated with dephasing processes. Fluctuating chaotic quantum systems are shown to exhibit extreme decoherence, with a rate that scales exponentially with the particle number, thus exceeding the polynomial dependence of systems with fluctuating k-body interactions. Our findings suggest the use of quantum chaotic systems as a natural test bed for spontaneous wave function collapse models. We further discuss the implications on the decoherence of AdS/CFT black holes resulting from the unitarity loss associated with energy dephasing. [less ▲] Detailed reference viewed: 22 (0 UL)Information Thermodynamics of Turing Patterns Falasco, Gianmaria ; Rao, Riccardo ; Esposito, Massimiliano in Physical Review Letters (2018) e set up a rigorous thermodynamic description of reaction-diffusion systems driven out of equilibrium by time-dependent space-distributed chemostats. Building on the assumption of local equilibrium ... [more ▼] e set up a rigorous thermodynamic description of reaction-diffusion systems driven out of equilibrium by time-dependent space-distributed chemostats. Building on the assumption of local equilibrium, nonequilibrium thermodynamic potentials are constructed exploiting the symmetries of the chemical network topology. It is shown that the canonical (resp. semigrand canonical) nonequilibrium free energy works as a Lyapunov function in the relaxation to equilibrium of a closed (resp. open) system and its variation provides the minimum amount of work needed to manipulate the species concentrations. The theory is used to study analytically the Turing pattern formation in a prototypical reaction-diffusion system, the one-dimensional Brusselator model, and to classify it as a genuine thermodynamic nonequilibrium phase transition. [less ▲] Detailed reference viewed: 265 (6 UL)Phonon-Polariton Mediated Thermal Radiation and Heat Transfer among Molecules and Macroscopic Bodies: Nonlocal Electromagnetic Response at Mesoscopic Scales ; ; Tkatchenko, Alexandre et al in Physical Review Letters (2018), 121 Detailed reference viewed: 157 (1 UL)Response functions as quantifiers of non-Markovianity Strasberg, Philipp ; Esposito, Massimiliano in Physical Review Letters (2018) Quantum non-Markovianity is crucially related to the study of dynamical maps, which are usually derived for initially factorized system-bath states. We here demonstrate that linear response theory also ... [more ▼] Quantum non-Markovianity is crucially related to the study of dynamical maps, which are usually derived for initially factorized system-bath states. We here demonstrate that linear response theory also provides a way to derive dynamical maps, but for initially correlated (and in general entangled) states. Importantly, these maps are always time-translational invariant and allow for a much simpler quantification of non-Markovianity compared to previous approaches. We apply our theory to the Caldeira-Leggett model, for which our quantifier is valid beyond linear response and can be expressed analytically. We find that a classical Brownian particle coupled to an Ohmic bath can already exhibit non-Markovian behaviour, a phenomenon related to the initial state preparation procedure. Furthermore, for a peaked spectral density we demonstrate that there is no monotonic relation between our quantifier and the system-bath coupling strength, the sharpness of the peak or the resonance frequency in the bath. [less ▲] Detailed reference viewed: 181 (3 UL)Dephasing in a Mach-Zehnder Interferometer by an Ohmic Contact Idrisov, Edvin ; ; in Physical Review Letters (2018) Detailed reference viewed: 202 (24 UL)Impact of many-body effects on Landau levels in graphene ; Reichardt, Sven ; Wirtz, Ludger et al in Physical Review Letters (2018), 120(18), 187701 We present magneto-Raman spectroscopy measurements on suspended graphene to investigate the charge carrier density-dependent electron-electron interaction in the presence of Landau levels. Utilizing gate ... [more ▼] We present magneto-Raman spectroscopy measurements on suspended graphene to investigate the charge carrier density-dependent electron-electron interaction in the presence of Landau levels. Utilizing gate-tunable magnetophonon resonances, we extract the charge carrier density dependence of the Landau level transition energies and the associated effective Fermi velocity vF. In contrast to the logarithmic divergence of vF at zero magnetic field, we find a piecewise linear scaling of vF as a function of the charge carrier density, due to a magnetic-field-induced suppression of the long-range Coulomb interaction. We quantitatively confirm our experimental findings by performing tight-binding calculations on the level of the Hartree-Fock approximation, which also allow us to estimate an excitonic binding energy of ≈6 meV contained in the experimentally extracted Landau level transitions energies. [less ▲] Detailed reference viewed: 189 (11 UL)Quantum-Mechanical Relation between Atomic Dipole Polarizability and the van der Waals Radius Fedorov, Dmitry ; Sadhukhan, Mainak ; Stoehr, Martin et al in Physical Review Letters (2018), 121 Detailed reference viewed: 336 (37 UL)Sadhukhan and Tkatchenko Reply Sadhukhan, Mainak ; Tkatchenko, Alexandre in Physical Review Letters (2018), 120 Detailed reference viewed: 233 (29 UL)Lattice model to derive the fluctuating hydrodynamics of active particles with inertia Manacorda, Alessandro in Physical Review Letters (2017) We derive the hydrodynamic equations with fluctuating currents for the density, momentum, and energy fields for an active system in the dilute limit. In our model, nonoverdamped self-propelled particles ... [more ▼] We derive the hydrodynamic equations with fluctuating currents for the density, momentum, and energy fields for an active system in the dilute limit. In our model, nonoverdamped self-propelled particles (such as grains or birds) move on a lattice, interacting by means of aligning dissipative forces and excluded volume repulsion. Our macroscopic equations, in a specific case, reproduce a transition line from a disordered phase to a swarming phase and a linear dispersion law accounting for underdamped wave propagation. Numerical simulations up to a packing fraction ∼ 10 % are in fair agreement with the theory, including the macroscopic noise amplitudes. At a higher packing fraction, a dense-diluted coexistence emerges. We underline the analogies with the granular kinetic theories, elucidating the relation between the active swarming phase and granular shear instability. [less ▲] Detailed reference viewed: 19 (0 UL)Critical Role of the Exchange Interaction for the Electronic Structure and Charge-Density-Wave Formation in TiSe2 ; ; et al in Physical Review Letters (2017), 119 We show that the inclusion of screened exchange via hybrid functionals provides a unified description of the electronic and vibrational properties of TiSe2. In contrast to local approximations in density ... [more ▼] We show that the inclusion of screened exchange via hybrid functionals provides a unified description of the electronic and vibrational properties of TiSe2. In contrast to local approximations in density functional theory, the explicit inclusion of exact, nonlocal exchange captures the effects of the electron-electron interaction needed to both separate the Ti-d states from the Se-p states and stabilize the charge-density- wave (CDW) (or low-T) phase through the formation of a p-d hybridized state. We further show that this leads to an enhanced electron-phonon coupling that can drive the transition even if a small gap opens in the high-T phase. Finally, we demonstrate that the hybrid functionals can generate a CDW phase where the electronic bands, the geometry, and the phonon frequencies are in agreement with experiments. [less ▲] Detailed reference viewed: 181 (7 UL)Effective Thermodynamics for a Marginal Observer Polettini, Matteo ; Esposito, Massimiliano in Physical Review Letters (2017), 119(24), Detailed reference viewed: 55 (1 UL)Strong Local-Field Enhancement of the Nonlinear Soft-Mode Response in a Molecular Crystal ; ; et al in Physical Review Letters (2017), 119 Detailed reference viewed: 187 (4 UL)Long-Range Repulsion Between Spatially Confined van der Waals Dimers Sadhukhan, Mainak ; Tkatchenko, Alexandre in Physical Review Letters (2017), 118 It is an undisputed textbook fact that nonretarded van der Waals (vdW) interactions between isotropic dimers are attractive, regardless of the polarizability of the interacting systems or spatial ... [more ▼] It is an undisputed textbook fact that nonretarded van der Waals (vdW) interactions between isotropic dimers are attractive, regardless of the polarizability of the interacting systems or spatial dimensionality. The universality of vdW attraction is attributed to the dipolar coupling between fluctuating electron charge densities. Here, we demonstrate that the long-range interaction between spatially confined vdW dimers becomes repulsive when accounting for the full Coulomb interaction between charge fluctuations. Our analytic results are obtained by using the Coulomb potential as a perturbation over dipole-correlated states for two quantum harmonic oscillators embedded in spaces with reduced dimensionality; however, the long-range repulsion is expected to be a general phenomenon for spatially confined quantum systems. We suggest optical experiments to test our predictions, analyze their relevance in the context of intermolecular interactions in nanoscale environments, and rationalize the recent observation of anomalously strong screening of the lateral vdW interactions between aromatic hydrocarbons adsorbed on metal surfaces. [less ▲] Detailed reference viewed: 394 (37 UL)Unifying Microscopic and Continuum Treatments of van der Waals and Casimir Interactions ; ; Tkatchenko, Alexandre et al in Physical Review Letters (2017), 118(1), 266802 We present an approach for computing long-range van der Waals (vdW) interactions between complex molecular systems and arbitrarily shaped macroscopic bodies, melding atomistic treatments of electronic ... [more ▼] We present an approach for computing long-range van der Waals (vdW) interactions between complex molecular systems and arbitrarily shaped macroscopic bodies, melding atomistic treatments of electronic fluctuations based on density functional theory in the former with continuum descriptions of strongly shape dependent electromagnetic fields in the latter, thus capturing many-body and multiple scattering effects to all orders. Such a theory is especially important when considering vdW interactions at mesoscopic scales, i.e., between molecules and structured surfaces with features on the scale of molecular sizes, in which case the finite sizes, complex shapes, and resulting nonlocal electronic excitations of molecules are strongly influenced by electromagnetic retardation and wave effects that depend crucially on the shapes of surrounding macroscopic bodies. We show that these effects together can modify vdW interaction energies and forces, as well as molecular shapes deformed by vdW interactions, by orders of magnitude compared to previous treatments based on Casimir-Polder, nonretarded, or pairwise approximations, which are valid only at macroscopically large or atomic-scale separations or in dilute insulating media, respectively. [less ▲] Detailed reference viewed: 372 (1 UL)Fluctuation-Dissipation Relations Far from Equilibrium Altaner, Bernhard ; Polettini, Matteo ; Esposito, Massimiliano in Physical Review Letters (2016), 117(180601), Near equilibrium, where all currents of a system vanish on average, the fluctuation-dissipation relation (FDR) connects a current’s spontaneous fluctuations with its response to perturbations of the ... [more ▼] Near equilibrium, where all currents of a system vanish on average, the fluctuation-dissipation relation (FDR) connects a current’s spontaneous fluctuations with its response to perturbations of the conjugate thermodynamic force. Out of equilibrium, fluctuation-response relations generally involve additional nondissipative contributions. Here, in the framework of stochastic thermodynamics, we show that an equilibriumlike FDR holds for internally equilibrated currents, if the perturbing conjugate force only affects the microscopic transitions that contribute to the current. We discuss the physical requirements for the validity of our result and apply it to nanosized electronic devices. [less ▲] Detailed reference viewed: 334 (12 UL)Thermal and electronic fluctuations of flexible adsorbed molecules: Azobenzene on Ag(111) ; ; Poltavskyi, Igor et al in Physical Review Letters (2016), 116 Detailed reference viewed: 215 (4 UL)How Far from Equilibrium Is Active Matter? Fodor, Etienne ; ; et al in PHYSICAL REVIEW LETTERS (2016), 117(3), Active matter systems are driven out of thermal equilibrium by a lack of generalized Stokes-Einstein relation between injection and dissipation of energy at the microscopic scale. We consider such a ... [more ▼] Active matter systems are driven out of thermal equilibrium by a lack of generalized Stokes-Einstein relation between injection and dissipation of energy at the microscopic scale. We consider such a system of interacting particles, propelled by persistent noises, and show that, at small but finite persistence time, their dynamics still satisfy a time-reversal symmetry. To do so, we compute perturbatively their steady-state measure and show that, for short persistent times, the entropy production rate vanishes. This endows such systems with an effective fluctuation-dissipation theorem akin to that of thermal equilibrium systems. Last, we show how interacting particle systems with viscous drags and correlated noises can be seen as in equilibrium with a viscoelastic bath but driven out of equilibrium by nonconservative forces, hence providing energetic insight into the departure of active systems from equilibrium. [less ▲] Detailed reference viewed: 28 (1 UL)Structural Transition in a Fluid of Spheroids: A Low-Density Vestige of Jamming ; ; et al in Physical Review Letters (2016), 116(9), A thermodynamically equilibrated fluid of hard spheroids is a simple model of liquid matter. In this model, the coupling between the rotational degrees of freedom of the constituent particles and their ... [more ▼] A thermodynamically equilibrated fluid of hard spheroids is a simple model of liquid matter. In this model, the coupling between the rotational degrees of freedom of the constituent particles and their translations may be switched off by a continuous deformation of a spheroid of aspect ratio t into a sphere (t=1). We demonstrate, by experiments, theory, and computer simulations, that dramatic nonanalytic changes in structure and thermodynamics of the fluids take place, as the coupling between rotations and translations is made to vanish. This nonanalyticity, reminiscent of a second-order liquid-liquid phase transition, is not a trivial consequence of the shape of an individual particle. Rather, free volume considerations relate the observed transition to a similar nonanalyticity at t=1 in structural properties of jammed granular ellipsoids. This observation suggests a deep connection to exist between the physics of jamming and the thermodynamics of simple fluids. © 2016 American Physical Society. [less ▲] Detailed reference viewed: 161 (10 UL) |
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