Fluctuation theorems (FTs), which describe some universal properties of nonequilibrium fluctuations, are examined from a quantum perspective and derived by introducing a two-point measurement on the system. FTs for closed and open systems driven out of equilibrium by an external time-dependent force, and for open systems maintained in a nonequilibrium steady state by nonequilibrium boundary conditions, are derived from a unified approach. Applications to fermion and boson transport in quantum junctions are discussed. Quantum master equations and Green's functions techniques for computing the energy and particle statistics are presented.
Accurate x-ray scattering techniques to measure the physical properties of dense plasmas have been developed for applications in high energy density physics. This class of experiments produces short-lived hot dense states of matter with electron densities in the range of solid density and higher where powerful penetrating x-ray sources have become available for probing. Experiments have employed laser-based x-ray sources that provide sufficient photon numbers in narrow bandwidth spectral lines, allowing spectrally resolved x-ray scattering measurements from these plasmas. The backscattering spectrum accesses the noncollective Compton scattering regime which provides accurate diagnostic information on the temperature, density, and ionization state. The forward scattering spectrum has been shown to measure the collective plasmon oscillations. Besides extracting the standard plasma parameters, density and temperature, forward scattering yields new observables such as a direct measure of collisions and quantum effects. Dense matter theory relates scattering spectra with the dielectric function and structure factors that determine the physical properties of matter. Applications to radiation-heated and shock-compressed matter have demonstrated accurate measurements of compression and heating with up to picosecond temporal resolution. The ongoing development of suitable x-ray sources and facilities will enable experiments in a wide range of research areas including inertial confinement fusion, radiation hydrodynamics, material science, or laboratory astrophysics.
Intermetallic compounds containing f-electron elements display a wealth of superconducting phases, which are prime candidates for unconventional pairing with complex order parameter symmetries. For instance, superconductivity has been found at the border of magnetic order as well as deep within ferromagnetically and antiferromagnetically ordered states, suggesting that magnetism may promote rather than destroy superconductivity. Superconducting phases near valence transitions or in the vicinity of magnetopolar order are candidates for new superconductive pairing interactions such as fluctuations of the conduction electron density or the crystal electric field, respectively. The experimental status of the study of the superconducting phases of f-electron compounds is reviewed.
The direct observation of spin structures with atomic-scale resolution, a long-time dream in condensed matter research, recently became a reality based on the development of spin-sensitive scanning probe methods, such as spin-polarized scanning-tunneling microscopy (SP-STM) and magnetic exchange force microscopy (MExFM). This article reviews the basic principles and methods of SP-STM and MExFM and describes recently achieved milestones in the application of these techniques to metallic and electrically insulating magnetic nanostructures. Discoveries of novel types of magnetic order at the nanoscale are presented as well as challenges for the future, including studies of local spin excitations based on spin-resolved inelastic tunneling spectroscopy and measurements of damping forces in MExFM experiments.
The structure and thermodynamic state of a system changes under the influence of external electric fields. Neutral systems are characterized by their dielectric constant epsilon, while charged ones also by their charge distribution. In this Colloquium several phenomena occurring in soft-matter systems in spatially uniform and nonuniform fields are surveyed and the role of the conductivity sigma and the linear or nonlinear dependency of epsilon on composition are identified. Uniform electric fields are responsible for elongation of droplets, for destabilization of interfaces between two liquids, and for mixing effects in liquid mixtures. Electric fields, when acting on phases with mesoscopic order, also give rise to block-copolymer orientation, to destabilization of polymer-polymer interfaces, and to order-order phase transitions. The role of linear and nonlinear dependences of epsilon on composition will be elucidated in these systems. In addition to the dielectric anisotropy, existence of a finite conductivity leads to appearance of large stresses when these systems are subject to external fields and usually to a reduction in the voltages required for the instabilities or phase transitions to occur. Finally, phase transitions which occur in nonuniform fields are described and emphasis on the importance of epsilon and sigma is given.
Intergalactic space is filled with a pervasive medium of ionized gas, the intergalactic medium (IGM). A residual neutral fraction is detected in the spectra of quasistellar objects at both low and high redshifts, revealing a highly fluctuating medium with temperatures characteristic of photoionized gas. The statistics of the fluctuations are well reproduced by numerical gravity-hydrodynamics simulations within the context of standard cosmological structure formation scenarios. Thus, the study of the IGM offers an opportunity to probe the nature of the primordial density fluctuations on scales unavailable to other methods. The simulations also suggest that the IGM is the dominant reservoir of baryons produced by the Big Bang, and so the principal source of the matter from which galaxies formed. The detection of metal systems within the IGM shows that it was enriched by evolved stars early in its history, demonstrating an intimate connection between galaxy formation and the IGM. A comprehensive review of the current understanding of the structure and physical properties of the IGM and its relation to galaxies is presented, concluding with comments on prospects for furthering the study of the IGM using future ground-based facilities and space-based experiments.
Complex (dusty) plasmas are composed of a weakly ionized gas and charged microparticles and represent the plasma state of soft matter. Complex plasmas have several remarkable features: Dynamical time scales associated with microparticles are "stretched" to tens of milliseconds, yet the microparticles themselves can be easily visualized individually. Furthermore, since the background gas is dilute, the particle dynamics in strongly coupled complex plasmas is virtually undamped, which provides a direct analogy to regular liquids and solids in terms of the atomistic dynamics. Finally, complex plasmas can be easily manipulated in different ways-also at the level of individual particles. Altogether, this gives us a unique opportunity to go beyond the limits of continuous media and study-at the kinetic level-various generic processes occurring in liquids or solids, in regimes ranging from the onset of cooperative phenomena to large strongly coupled systems. In the first part of the review some of the basic and new physics are highlighted which complex plasmas enable us to study, and in the second (major) part strong coupling phenomena in an interdisciplinary context are examined. The connections with complex fluids are emphasized and a number of generic liquid and solid-state issues are addressed. In summary, application oriented research is discussed.
Recent progress in the field of a versatile and common system in soft matter physics, namely, star-shaped polyelectrolytes, is reviewed. These charged macromolecules combine in their properties aspects of polymer physics, colloidal science, and the rich physics of charged matter, rendering them into versatile building blocks for new materials as well as prototypes for studying the effects of softness in the behavior of colloidal suspensions. The approaches to the problem are manifold. Theoretical methods typically involve scaling theory, self-consistent field theory, and variational free-energy calculations, while computer simulations play an important role in enhancing our understanding of the physics involved. Experiments, based mostly on scattering, offer insights from a different point of view. Finally, the flexibility in the synthesis of novel types of macromolecules has added to the richness and the increased activity in the field in the last few years. This review puts emphasis on theory and simulation but takes into account the key experimental findings in critically discussing the merits and shortcomings of the former. The perspectives opened for the future, with emphasis on the possibilities to steer the behavior of novel materials, are also discussed.
Effective field theory allows for a systematic and model-independent derivation of the forces between nucleons in harmony with the symmetries of quantum chromodynamics. The foundations of this approach are reviewed and its application for light nuclei at various resolution scales is discussed. The extension of this approach to many-body systems is sketched.
Equilibrium phase transitions may be defined as nonanalytic points of thermodynamic functions, e.g., of the canonical free energy. Given a certain physical system, it is of interest to understand which properties of the system account for the presence, or the absence, of a phase transition, and an investigation of these properties may lead to a deeper understanding of the physical phenomenon. One possible way to approach this problem, reviewed and discussed in the present paper, is the study of topology changes in configuration space which are found to be related to equilibrium phase transitions in classical statistical mechanical systems. For the study of configuration space topology, one considers the subsets M-v, consisting of all points from configuration space with a potential energy per particle equal to or less than a given v. For finite systems, topology changes of M-v are intimately related to nonanalytic points of the microcanonical entropy. In the thermodynamic limit, a more complex relation between nonanalytic points of thermodynamic functions (i.e., phase transitions) and topology changes is observed. For some class of short-range systems, a topology change of the M-v at v=v(t) was proven to be necessary, but not sufficient, for a phase transition to take place at a potential energy v(t). In contrast, phase transitions in systems with long-range interactions or in systems with nonconfining potentials need not be accompanied by such a topology change. Instead, for such systems the nonanalytic point in a thermodynamic function is found to have some maximization procedure at its origin. These results may foster insight into the mechanisms which lead to the occurrence of a phase transition, and thus may help to explore the origin of this physical phenomenon.
This paper presents a review on the field of inclusive quasielastic electron-nucleus scattering. It discusses the approach used to measure the data and includes a compilation of data available in numerical form. The theoretical approaches used to interpret the data are presented. A number of results obtained from the comparison between experiment and calculation are then reviewed. The analogies to, and differences from, other fields of physics exploiting quasielastic scattering from composite systems are pointed out.
Disclinations were first observed in mesomorphic phases. They were later found relevant to a number of ill-ordered condensed-matter media involving continuous symmetries or frustrated order. Disclinations also appear in polycrystals at the edges of grain boundaries; but they are of limited interest in solid single crystals, where they can move only by diffusion climb and, owing to their large elastic stresses, mostly appear in close pairs of opposite signs. The relaxation mechanisms associated with a disclination in its creation, motion, and change of shape involve an interplay with continuous or quantized dislocations and/or continuous disclinations. These are attached to the disclinations or are akin to Nye's dislocation densities, which are particularly well suited for consideration here. The notion of an extended Volterra process is introduced, which takes these relaxation processes into account and covers different situations where this interplay takes place. These concepts are illustrated by a variety of applications in amorphous solids, mesomorphic phases, and frustrated media in their curved habit space. These often involve disclination networks with specific node conditions. The powerful topological theory of line defects considers only defects stable against any change of boundary conditions or relaxation processes compatible with the structure considered. It can be seen as a simplified case of the approach considered here, particularly suited for media of high plasticity or/and complex structures. It cannot analyze the dynamical properties of defects nor the elastic constants involved in their static properties; topological stability cannot guarantee energetic stability, and sometimes cannot distinguish finer details of the structure of defects.
This review provides a perspective on the use of orbital-dependent functionals, which is currently considered one of the most promising avenues in modern density-functional theory. The focus here is on four major themes: the motivation for orbital-dependent functionals in terms of limitations of semilocal functionals; the optimized effective potential as a rigorous approach to incorporating orbital-dependent functionals within the Kohn-Sham framework; the rationale behind and advantages and limitations of four popular classes of orbital-dependent functionals; and the use of orbital-dependent functionals for predicting excited-state properties. For each of these issues, both formal and practical aspects are assessed.
The progress in solving problems involving nonrelativistic fast ion (atom)-atom collisions with two actively participating electrons is reviewed. Such processes involve, e.g., (i) scattering between a bare nucleus (projectile) P of charge Z(P) and a heliumlike atomic system consisting of two electrons e(1) and e(2) initially bound to the target nucleus T of charge Z(T), i.e., the Z(P)-(Z(T);e(1),e(2))(i) collisions; (ii) scattering between two hydrogenlike atoms (Z(P),e(1))(i1) and (Z(T),e(2))(i2), etc. A proper description of these collisional processes requires solutions of four-body problems with four active particles including two nuclei and two electrons. Among various one- as well as two-electron transitions which can occur in such collisions, special attention will be paid to double-electron capture, simultaneous transfer and ionization, simultaneous transfer and excitation, single-electron detachment and single-electron capture. Working within the four-body framework of scattering theory and imposing the proper Coulomb boundary conditions on the entrance and exit channels, the leading quantum-mechanical theories are analyzed. Both static and dynamic interelectron correlations are thoroughly examined. The correct links between scattering states and perturbation potentials are strongly emphasized. Selection of the present illustrations is dictated by the importance of interdisciplinary applications of energetic ion-atom collisions, ranging from thermonuclear fusion to medical accelerators for hadron radiotherapy.
The flow of fluids in channels, pipes, or ducts, as in any other wall-bounded flow (like water along the hulls of ships or air on airplanes) is hindered by a drag, which increases manyfold when the fluid flow turns from laminar to turbulent. A major technological problem is how to reduce this drag in order to minimize the expense of transporting fluids like oil in pipelines, or to move ships in the ocean. It was discovered that minute concentrations of polymers can reduce the drag in turbulent flows by up to 80%. While experimental knowledge had accumulated over the years, the fundamental theory of drag reduction by polymers remained elusive for a long time, with arguments raging whether this is a "skin" or a "bulk" effect. In this Colloquium the phenomenology of drag reduction by polymers is summarized, stressing both its universal and nonuniversal aspects, and a recent theory is reviewed that provides a quantitative explanation of all the known phenomenology. Both flexible and rodlike polymers are treated, explaining the existence of universal properties like the maximum drag reduction asymptote, as well as nonuniversal crossover phenomena that depend on the Reynolds number, on the nature of the polymer and on its concentration. Finally other agents for drag reduction are discussed with a stress on the important example of bubbles.
High-harmonic generation provides an attractive light source of coherent radiation in the extreme-ultraviolet (XUV) and soft-x-ray regions of the spectrum and allows for the production of single attosecond pulses or pulse trains. This Colloquium covers the control of high-harmonic spectra by temporal and spatial pulse shaping of the driving laser pulses and its implications on time-resolved XUV spectroscopy and attosecond pulse shaping. It summarizes important steps for extending existing pulse shaping techniques and control schemes from the near-infrared or visible part to shorter wavelengths. Using adaptive pulse shaping of the driving laser pulses, several groups have demonstrated control of the high-harmonic spectrum, including the author's work on the complete control over the XUV spectrum of high-order harmonics, generated in a gas-filled hollow fiber. It is possible to achieve both the enhancement and the suppression of single or several selected harmonic orders. These arbitrarily shaped soft-x-ray spectra will allow for important modifications of the resulting harmonic pulses in the temporal domain. This constitutes first steps towards direct attosecond pulse shaping in the soft-x-ray domain. Moreover, high-harmonic generation in a hollow-core fiber can be enhanced by coupling into a single fiber mode using a feedback-controlled adaptive two-dimensional spatial light modulator.
With the continued improvement of sequencing technologies, the prospect of genome-based medicine is now at the forefront of scientific research. To realize this potential, however, a revolutionary sequencing method is needed for the cost-effective and rapid interrogation of individual genomes. This capability is likely to be provided by a physical approach to probing DNA at the single-nucleotide level. This is in sharp contrast to current techniques and instruments that probe (through chemical elongation, electrophoresis, and optical detection) length differences and terminating bases of strands of DNA. Several physical approaches to DNA detection have the potential to deliver fast and low-cost sequencing. Central to these approaches is the concept of nanochannels or nanopores, which allow for the spatial confinement of DNA molecules. In addition to their possible impact in medicine and biology, the methods offer ideal test beds to study open scientific issues and challenges in the relatively unexplored area at the interface between solids, liquids, and biomolecules at the nanometer length scale. This Colloquium emphasizes the physics behind these methods and ideas, critically describes their advantages and drawbacks, and discusses future research opportunities in the field.
Maxwell's demon was born in 1867 and still thrives in modern physics. He plays important roles in clarifying the connections between two theories: thermodynamics and information. Here the history of the demon and a variety of interesting consequences of the second law of thermodynamics are presented, mainly in quantum mechanics, but also in the theory of gravity. Also highlighted are some of the recent work that explores the role of information, illuminated by Maxwell's demon, in the arena of quantum-information theory.