Study Of Nonequilibrium Phenomena Research Articles

Rectification and confinement of photokinetic bacteria in an optical feedback loop

Active particles can self-propel by exploiting locally available energy resources. When powered by light, these resources can be distributed with high resolution allowing spatio-temporal modulation of motility. Here we show that the random walks of light-driven bacteria are rectified when they swim in a structured light field that is obtained by a simple geometric transformation of a previous system snapshot. The obtained currents achieve an optimal value that we establish by general theoretical arguments. This optical feedback is used to gather and confine bacteria in high-density and high-activity regions that can be dynamically relocated and reconfigured. Moving away from the boundaries of these optically confined states, the density decays to zero in a few tens of micrometers, exhibiting steep exponential tails that suppress cell escape and ensure long-term stability. Our method is general and scalable, providing a versatile tool to produce localized and tunable active baths for microengineering applications and systematic studies of non-equilibrium phenomena in active systems.

Time-Dependent Gutzwiller Approximation: Theory and Applications

The time-dependent Gutzwiller approximation is rederived on the basis of a variational wave function which is a direct product of a Slater determinant and a coherent state. The latter can be related to the slave-boson formulation by Kotliar and Ruckenstein, and our approach offers a convenient way to generalize the theory towards the implementation of symmetry-broken states and the study of non-equilibrium phenomena. We discuss the concept with regard to applications in the linear response limit and for quenched antiferromagnetic order for which we evaluate the optical conductivity in non-equilibrium situations.

20th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON 20)

The 20th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures (EDISON 20) was held at the Hyatt Regency Hotel and Conference Center in downtown Buffalo, New York, USA from July 17–21, 2017. The meeting serves as the premier forum for researchers working on the study of nonequilibrium phenomena in semiconductors, from all parts of the globe, and was organized locally by faculty at the University at Buffalo and the University of Rochester.EDISON is an international conference series with biennial meetings that cover recent progress in the field of electron dynamics in solid-state materials and devices. Initially established with the title Hot Carriers in Semiconductors (HCIS), the first meeting took place in Modena, Italy in 1973. The name was changed to International Conference on Nonequilibrium Carrier Dynamics in Semiconductors at the 1997 Berlin meeting, and again at the 2009 meeting in Montpellier to the current form. Since then, EDISON conferences have been held in Santa Barbara, USA (2011); Matsue, Japan (2013); Salamanca, Spain (2015); and Buffalo, USA (2017).The EDISON 20 program included 12 invited talks, 50 oral contributions, 116 accepted abstracts, and one special seminar. In total, 152 participants from 22 countries gathered to share and exchange ideas and recent results. Approximately 45% of the participants were from North America, 30% from Europe, and 25% from the Asia Pacific region. Fully 30% of the participants were students, and there was a very good balance between experimental and theoretical approaches. Topics with the most contributions were: Electronic and optical properties of graphene and other 2D materials; Nonequilibrium carrier transport; and Terahertz phenomena in semiconductor materials and devices.I thank all the members of the Program Committee and the International Advisory Committee for their valuable input, as well as Professor Jonathan Bird and Alex Desha for their many hours devoted to organizing a successful EDISON conference. Also critical to the success of the conference is financial support, so I thank the School of Engineering and Applied Sciences, the Vice President for Research and Economic Development, the Department of Physics, and the Department of Electrical Engineering at the University at Buffalo, as well as the U.S. Department of Energy, Kurt J. Lesker Company, and the Hajim School of Engineering & Applied Sciences at the University of Rochester for their sponsorship of EDISON 20. Finally, I thank all the scientists who contributed to the preparation and peer-review of these proceedings.Erik Einarsson, EditorEDISON 20 Publications ChairUniversity at Buffalo

Quantum transport in ultracold atoms

Ultracold atoms confined by engineered magnetic or optical potentials are ideal systems for studying phenomena otherwise difficult to realize or probe in the solid state because their atomic interaction strength, number of species, density, and geometry can be independently controlled. This review focuses on quantum transport phenomena in atomic gases that mirror and oftentimes either better elucidate or show fundamental differences with those observed in mesoscopic and nanoscopic systems. We discuss significant progress in performing transport experiments in atomic gases, contrast similarities and differences between transport in cold atoms and in condensed matter systems, and survey inspiring theoretical predictions that are difficult to verify in conventional setups. These results further demonstrate the versatility offered by atomic systems in the study of nonequilibrium phenomena and their promise for novel applications.

Nonequilibrium dynamical mean-field theory and its applications

The study of nonequilibrium phenomena in correlated lattice systems has developed into an active and exciting branch of condensed matter physics. This research field provides rich new insights that could not be obtained from the study of equilibrium situations, and the theoretical understanding of the physics often requires the development of new concepts and methods. On the experimental side, ultra-fast pump-probe spectroscopies enable studies of excitation and relaxation phenomena in correlated electron systems, while ultra-cold atoms in optical lattices provide a new way to control and measure the time-evolution of interacting lattice systems with a vastly different characteristic timescale compared to electron systems. A theoretical description of these phenomena is challenging because, firstly, we have to compute the quantum-mechanical time-evolution of many-body systems out of equilibrium, and secondly, deal with strong-correlation effects which can be of nonperturbative nature. In this review, we discuss the nonequilibrium extension of the dynamical mean field theory (DMFT), which treats quantum fluctuations in the time domain and works directly in the thermodynamic limit. The method reduces the complexity of the calculation via a mapping to a self-consistent impurity problem. Particular emphasis is placed on a detailed derivation of the formalism, and on a discussion of numerical techniques, which enable solutions of the effective nonequilibrium DMFT impurity problem. We summarize the insights gained into the properties of the infinite-dimensional Hubbard model under strong non-equilibrium conditions. These examples illustrate the current ability of the theoretical framework to reproduce and understand fundamental nonequilibrium phenomena, such as the dielectric breakdown of Mott insulators, photo-doping, and collapse-and-revival oscillations in quenched systems.

Thermodynamics of stationary states

In the study of nonequilibrium phenomena, improving on near-equilibrium linear approximations has long been a major goal. Over the past ten years, in collaboration with Bertini, De Sole, Gabrielli and Landim, we developed a general approach to nonequilibrium diffusive systems known as Macroscopic Fluctuation Theory, making some progress in this direction. Our theory has been inspired by stochastic models of interacting particles (stochastic lattice gases). It is based on the study of rare fluctuations of macroscopic variables in stationary states and leads to interesting new results and predictions. This paper gives a compact presentation of the theory with some applications.

Device for the study of nonequilibrium phenomena in semiconductor structures

A device for studying the relaxation dynamics of nonequilibrium capacitance and charge in the mode of nonequilibrium depletion of MIS structures is designed. Methods of measurements were developed that provide a sensitivity of 0.03 pF and 0.02 pC along the capacitance and charge measurement channels with the acceleration time 1.5 µs and 0.7 µs, respectively. The results are obtained with a double amplitude of the test signal of capacitance measurement of ∼15 mV and frequency 5 MHz. A mode of measuring the capacitance-voltage characteristics with a scanning duration up to 100 s is implemented.

Extended Clausius Relation and Entropy for Nonequilibrium Steady States in Heat Conducting Quantum Systems

Recently, in their attempt to construct steady state thermodynamics (SST), Komatsu, Nakagawa, Sasa, and Tasaki found an extension of the Clausius relation to nonequilibrium steady states in classical stochastic processes. Here we derive a quantum mechanical version of the extended Clausius relation. We consider a small system of interest attached to large systems which play the role of heat baths. By only using the genuine quantum dynamics, we realize a heat conducting nonequilibrium steady state in the small system. We study the response of the steady state when the parameters of the system are changed abruptly, and show that the extended Clausius relation, in which “heat” is replaced by the “excess heat”, is valid when the temperature difference is small. Moreover we show that the entropy that appears in the relation is similar to von Neumann entropy but has an extra symmetrization with respect to time-reversal. We believe that the present work opens a new possibility in the study of nonequilibrium phenomena in quantum systems, and also confirms the robustness of the approach by Komatsu et al.

Statistical-Thermodynamic Study of Nonequilibrium Phenomena in Three-dimensional Anharmonic Crystal Lattices: IV. Elastic Constants and Free Energy of Elastic Solids

Thermodynamic quantities of elastic solids such as elastic constants, specific heats, coefficients of thermal expansion and Gruneisen parameters are analyzed and discussed by using the linearized macroscopic basic equations proposed in the former paper of the present series. Furthermore some coefficients which relate thermal vibrations of constituent atoms to temperature variation and strain are studied. Then the Helmholtz free energy of elastic solids is formulated explicitly.

Dynamical chaos in the Lorentz lattice gas

This paper provides an introduction to the applications of dynamical systems theory to nonequilibrium statistical mechanics, in particular to a study of nonequilibrium phenomena in Lorentz lattice gases with stochastic collision rules. Using simple arguments, based upon discussions in the mathematical literature, we show that such lattice gases belong to the category of dynamical systems with positive Lyapunov exponents. This is accomplished by showing how such systems can be expressed in terms of continuous phase space variables. Expressions for the Lyapunov exponent of a one-dimensional Lorentz lattice gas with periodic boundaries are derived. Other quantities of interest for the theory of irreversible processes are discussed.

A study of non-equilibrium phenomena in linear-sweep MIS capacitors

Under an inversion bias and in response to a linear voltage sweep, the capacitance voltage (C-V) and current-voltage (C-V) characteristics of metal-insulator-semiconductor (MIS) capacitors are described and discussed. An improved model for the generation width is applied, in which the effect of inversion minority carriers on the minority quasi-Fermi level has been taken into account. A differential equation is developed with which to describe the change of the depletion region under the linear voltage sweep. The high-frequency MIS capacitance and gate current are related to the depletion region width. In this way the non-equilibrium characteristics of linear-sweep MIS capacitors are described.

Dynamical block analysis in a non-equilibrium system

We present molecular dynamics simulation results of quenches into the unstable region of a two-dimensional Lennard-Jones system. The evolution of the system from the non-equilibrium state into equilibrium was analyzed with a dynamical block analysis. This can lead to a new approach in the study of non-equilibrium phenomena. We show that with such an analysis one can obtain results on the dynamic evolution as the system evolves, consistent with those obtained from and analysis of the pair-distribution function, structure factor and excess energy. The simulations were carried out on the parallel computer of the condensed matter theory group at the University of Mainz.

Исследование неравновесных явлении в ударных волнах

Исследование неравновесных явлении в ударных волнах