![]() Falasco, Gianmaria ![]() ![]() in Physical Review Letters (2020), 125(12), 120604 Detailed reference viewed: 14 (0 UL)![]() ; ; et al in Physical Review Letters (2020), 125 Detailed reference viewed: 53 (2 UL)![]() ; Toulouse, Constance ![]() in PHYSICAL REVIEW LETTERS (2020), 124(9), 097603-6 Model materials are precious test cases for elementary theories and provide building blocks for the understanding of more complex cases. Here, we describe the lattice dynamics of the structural phase ... [more ▼] Model materials are precious test cases for elementary theories and provide building blocks for the understanding of more complex cases. Here, we describe the lattice dynamics of the structural phase transition in francisite Cu3Bi(SeO3)(2)O2Cl at 115 K and show that it provides a rare archetype of a transition driven by a soft antipolar phonon mode. In the high-symmetry phase at high temperatures, the soft mode is found at (0,0,0.5) at the Brillouin zone boundary and is measured by inelastic x-ray scattering and thermal diffuse scattering. In the low-symmetry phase, this soft-mode is folded back onto the center of the Brillouin zone as a result of the doubling of the unit cell, and appears as a fully symmetric mode that can be tracked by Raman spectroscopy. On both sides of the transition, the mode energy squared follows a linear behavior over a large temperature range. First-principles calculations reveal that, surprisingly, the flat phonon band calculated for the high-symmetry phase seems incompatible with the displacive character found experimentally. We discuss this unusual behavior in the context of an ideal Kittel model of an antiferroelectric transition. [less ▲] Detailed reference viewed: 21 (3 UL)![]() ; Toulouse, Constance ![]() in Physical Review Letters (2020) Detailed reference viewed: 13 (0 UL)![]() ; ; Cavina, Vasco ![]() in Physical Review Letters (2020), 124(17), 170603 Detailed reference viewed: 30 (4 UL)![]() ; Esposito, Massimiliano ![]() in Physical Review Letters (2020), 124(25), 250603 Detailed reference viewed: 21 (2 UL)![]() ; Tkatchenko, Alexandre ![]() in Physical Review Letters (2020) Detailed reference viewed: 46 (1 UL)![]() ; Tkatchenko, Alexandre ![]() in Physical Review Letters (2020) Detailed reference viewed: 22 (0 UL)![]() ; Esposito, Massimiliano ![]() in PHYSICAL REVIEW LETTERS (2019) Detailed reference viewed: 68 (1 UL)![]() ; Iñiguez, Jorge ![]() in PHYSICAL REVIEW LETTERS (2019), 123(18), Detailed reference viewed: 31 (1 UL)![]() ; ; Sengupta, Anupam ![]() in Physical Review Letters (2019), 123(17-25), The transition from monolayers to multilayered structures in bacterial colonies is a fundamental step in biofilm development. Observed across different morphotypes and species, this transition is ... [more ▼] The transition from monolayers to multilayered structures in bacterial colonies is a fundamental step in biofilm development. Observed across different morphotypes and species, this transition is triggered within freely growing bacterial microcolonies comprising a few hundred cells. Using a combination of numerical simulations and analytical modeling, here we demonstrate that this transition originates from the competition between growth-induced in-plane active stresses and vertical restoring forces, due to the cell-substrate interactions. Using a simple chainlike colony of laterally confined cells, we show that the transition sets when individual cells become unstable to rotations; thus it is localized and mechanically deterministic. Asynchronous cell division renders the process stochastic, so that all the critical parameters that control the onset of the transition are continuously distributed random variables. Here we demonstrate that the occurrence of the first division in the colony can be approximated as a Poisson process in the limit of large cell numbers. This allows us to approximately calculate the probability distribution function of the position and time associated with the first extrusion. The rate of such a Poisson process can be identified as the order parameter of the transition, thus highlighting its mixed deterministic-stochastic nature. [less ▲] Detailed reference viewed: 48 (1 UL)![]() Schmidt, Thomas ![]() in Physical Review Letters (2019), 123 We study a one-dimensional interacting quantum liquid hosting a pair of mobile impurities causing backscattering. We determine the effective retarded interaction between the two impurities mediated by the ... [more ▼] We study a one-dimensional interacting quantum liquid hosting a pair of mobile impurities causing backscattering. We determine the effective retarded interaction between the two impurities mediated by the liquid. We show that for strong backscattering this interaction gives rise to resonances and antiresonances in the finite-frequency mobility of the impurity pair. At the antiresonances, the two impurities remain at rest even when driven by a (small) external force. At the resonances, their synchronous motion follows the external drive in phase and reaches maximum amplitude. Using a perturbative renormalization group analysis in quantum tunneling across the impurities, we study the range of validity of our model. We predict that these mechanical antiresonances are observable in experiments on ultracold atom gases confined to one dimension. [less ▲] Detailed reference viewed: 86 (0 UL)![]() ; ; Tian, Haoye ![]() in PHYSICAL REVIEW LETTERS (2019), 122(24), Detailed reference viewed: 61 (12 UL)![]() ; ; et al in PHYSICAL REVIEW LETTERS (2019), 122(22), Detailed reference viewed: 27 (1 UL)![]() Paleari, Fulvio ![]() 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: 139 (8 UL)![]() ; Torun, Engin ![]() ![]() 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: 103 (8 UL)![]() ; ; et al in Physical Review Letters (2019), 122(14), We present a statistical analysis of the experimental trajectories of colloids in a dilute suspension of the green algae Chlamydomonas reinhardtii. The measured probability density function (pdf) of the ... [more ▼] We present a statistical analysis of the experimental trajectories of colloids in a dilute suspension of the green algae Chlamydomonas reinhardtii. The measured probability density function (pdf) of the displacements of colloids covers 7 orders of magnitude. The pdfs are characterized by non-Gaussian tails for intermediate time intervals, but nevertheless they collapse when scaled with their standard deviation. This diffusive scaling breaks down for longer time intervals and the pdf becomes Gaussian. However, the mean squared displacements of tracer positions are linear over the complete measurement time interval. Experiments are performed for various tracer diameters, swimmer concentrations, and mean swimmer velocities. This allows a rigorous comparison with several theoretical models. We can exclude a description based on an effective temperature and other mean field approaches that describe the irregular motion as a sum of the fluctuating far field of many microswimmers. The data are best described by the microscopic model by J.-L. Thiffeault, Distribution of particle displacements due to swimming microorganisms, Phys. Rev. E 92, 023023 (2015). [less ▲] Detailed reference viewed: 30 (0 UL)![]() ; Esposito, Massimiliano ![]() in Physical Review Letters (2019), 122(15), Detailed reference viewed: 68 (2 UL)![]() Falasco, Gianmaria ![]() ![]() ![]() 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: 229 (6 UL)![]() ; ; Tkatchenko, Alexandre ![]() in Physical Review Letters (2018), 121 Detailed reference viewed: 135 (1 UL) |
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