Showing papers in "Physics-Uspekhi in 2010"

Nonlinear aspects of quantum plasma physics

Abstract: Dense quantum plasmas are ubiquitous in planetary interiors and in compact astrophysical objects (e.g., the interior of white dwarf stars, in magnetars, etc.), in semiconductors and micromechanical systems, as well as in the next-generation intense laser–solid density plasma interaction experiments and in quantum X-ray free-electron lasers. In contrast to classical plasmas, quantum plasmas have extremely high plasma number densities and low temperatures. Quantum plasmas are composed of electrons, positrons and holes, which are degenerate. Positrons (holes) have the same (slightly different) mass as electrons, but opposite charge. The degenerate charged particles (electrons, positrons, and holes) obey the Fermi–Dirac statistics. In quantum plasmas, there are new forces associated with (i) quantum statistical electron and positron pressures, (ii) electron and positron tunneling through the Bohm potential, and (iii) electron and positron angular momentum spin. Inclusion of these quantum forces allows the existence of very high-frequency dispersive electrostatic and electromagnetic waves (e.g., in the hard X-ray and gamma-ray regimes) with extremely short wavelengths. In this review paper, we present theoretical backgrounds for some important nonlinear aspects of wave–wave and wave–electron interactions in dense quantum plasmas. Specifically, we focus on nonlinear electrostatic electron and ion plasma waves, novel aspects of three-dimensional quantum electron fluid turbulence, as well as nonlinearly coupled intense electromagnetic waves and localized plasma wave structures. Also discussed are the phase-space kinetic structures and mechanisms that can generate quasistationary magnetic fields in dense quantum plasmas. The influence of the external magnetic field and the electron angular momentum spin on the electromagnetic wave dynamics is discussed. Finally, future perspectives of the nonlinear quantum plasma physics are highlighted.

Superconductor-insulator quantum phase transition

Abstract: The current understanding of the superconductor–insulator transition is discussed level by level in a cyclic spiral-like manner. At the first level, physical phenomena and processes are discussed which, while of no formal relevance to the topic of transitions, are important for their implementation and observation; these include superconductivity in low electron density materials, transport and magnetoresistance in superconducting island films and in highly resistive granular materials with superconducting grains, and the Berezinskii–Kosterlitz–Thouless transition. The second level discusses and summarizes results from various microscopic approaches to the problem, whether based on the Bardeen–Cooper–Schrieffer theory (the disorder-induced reduction in the superconducting transition temperature; the key role of Coulomb blockade in high-resistance granular superconductors; superconducting fluctuations in a strong magnetic field) or on the theory of the Bose–Einstein condensation. A special discussion is given to phenomenological scaling theories. Experimental investigations, primarily transport measurements, make the contents of the third level and are for convenience classified by the type of material used (ultrathin films, variable composition materials, high-temperature superconductors, superconductor–poor metal transitions). As a separate topic, data on nonlinear phenomena near the superconductor–insulator transition are presented. At the final, summarizing, level the basic aspects of the problem are enumerated again to identify where further research is needed and how this research can be carried out. Some relatively new results, potentially of key importance in resolving the remaining problems, are also discussed.

Current trends in the physics of thermoelectric materials

Abstract: Basic physical ideas and methods that are used to improve the quality of modern thermoelectric materials and to increase the thermoelectric figure-of-merit are reviewed, with special emphasis on how nanostructure affects the thermoelectric properties of materials.

Surface states in photonic crystals

Abstract: The propagation of surface electromagnetic waves along photonic crystal (PC) boundaries is examined. It is shown that in a number of cases, these are backward waves. The nature of surface electromagnetic states localized at the PC boundary is discussed; these states transfer no energy along the boundary (their tangential wave number is zero). An analogy with the well-known Tamm and Shockley surface states in solid state physics is drawn. It is shown that in the case of a PC, both types of states can be regarded as Tamm states. Experimental results on the observation of surface states are presented. A system using an external magnetic field to control a surface state is considered.

Nonlocal electron kinetics in gas-discharge plasma

Abstract: The field of electron kinetics in extremely nonequilibrium glow discharge plasma is reviewed, starting from the classical works of Langmuir. It is shown that it is only in terms of kinetics that many aspects of nonequilibrium plasma — such as the structure of near-electrode regions, spatial profiles of ionization and luminosity, striations and particle and energy flows — can be adequately understood.

Carbon nanotube-based electron field emitters

Abstract: The current status of research and development of carbon nanotubes (CNTs) electron field emitters is reviewed. The physical aspects of electron field emission that underlie the unique emission properties of CNTs are considered. Physical effects and phenomena affecting the emission characteristics of CNT cathodes are analyzed. Effects given particular attention include the electric field enhancement near a CNT tip; electric field screening by neighboring nanotubes; statistical spread of the parameters of the individual CNTs comprising the cathode; the effects of heat leading to thermal degradation of nanotubes during emission, and adsorbate effects on the surface of the emitter. Advances in vacuum electronics due to the use of CNT field cathodes are reviewed.

Magnetohydrodynamic models of astrophysical jets

Abstract: In this review, analytical results obtained for a wide class of stationary axisymmetric flows in the vicinity of compact astrophysical objects are analyzed, with an emphasis on quantitative predictions for specific sources. Recent years have witnessed a great increase in understanding the formation and properties of astrophysical jets. This is due not only to new observations but also to advances in analytical theory which has produced fairly simple relations, and to what can undoubtedly be called a breakthrough in numerical simulation which has enabled confirmation of theoretical predictions. Of course, we are still very far from fully understanding the physical processes occurring in compact sources. Nevertheless, the progress made raises hopes for near-future test observations that can give insight into the physical processes occurring in active astrophysical objects.

The physics of neutron stars

Abstract: Topical problems in the physics of and basic facts about neutron stars are reviewed. The observational manifestations of neutron stars, their core and envelope structure, magnetic fields, thermal evolution, and masses and radii are briefly discussed, along with the underlying microphysics.

Physical conditions in potential accelerators of ultra-high-energy cosmic rays: updated Hillas plot and radiation-loss constraints

Abstract: We review basic constraints on the acceleration of ultra-high-energy (UHE) cosmic rays (CRs) in astrophysical sources, namely, the geometric (Hillas) criterion and the restrictions from radiation losses in different acceleration regimes Using the latest available astrophysical data, we redraw the Hillas plot and find potential UHECR accelerators For the acceleration in the central engines of active galactic nuclei, we constrain the maximal UHECR energy for a given black hole mass Among active galaxies, only the most powerful ones, radio galaxies and blazars, are able to accelerate protons to UHE, although acceleration of heavier nuclei is possible in much more abundant lower-power Seyfert galaxies

Small-angle neutron scattering in structure research of magnetic fluids

Abstract: A magnetic fluid (MF) is a liquid dispersion of magnetic nanoparticles coated by surfactants for stabilization The MF research reviewed in this paper is primarily aimed at investigating the atomic and magnetic structure of MF particles and the way they interact under various conditions by means of small-angle neutron scattering (SANS) The presence of a liquid carrier in the structure and the magnetic properties of MFs, which are very close to those of an ideal superparamagnetic system, allow the effective use of the major neutron scattering features: the strong effect of hydrogen–deuterium isotopic substitution and magnetic scattering An extension of the contrast variation technique to the structure research on polydisperse and superparamagnetic systems is proposed The cases of noninteracting and interacting particles, the latter with cluster formation taken into account, are considered for non-magnetized and magnetized MFs The polarized neutron scattering analysis of the structure of magnetized MFs is illustrated by examples Topical problems in further developing the method to study multiparameter systems are identified

Fascination of chaos

Abstract: This review introduces most of the concepts used in the study of chaotic phenomena in nonlinear systems and has as its objective to summarize the current understanding of results from the theory of chaotic dynamical systems and to describe the original ideas underlying the study of deterministic chaos. The presentation relies on informal analysis, with abstract mathematical ideas visualized geometrically or by examples from physics. Hyperbolic dynamics, homoclinic trajectories and tangencies, wild hyperbolic sets, and different types of attractors which appear in dynamical systems are considered. The key aspects of ergodic theory are discussed, and the basic statistical properties of chaotic dynamical systems are described. The fundamental difference between stochastic dynamics and deterministic chaos is explained. The review concludes with an investigation of the possibility of studying complex systems on the basis of the analysis of registered signals, i.e. the generated time series.

Application and electronic structure of high-permittivity dielectrics

Abstract: Major applications of high-permittivity dielectric materials in silicon devices are reviewed. The basics and software implementations of the electron density functional method are considered. Results of first-principle calculations of the electronic structure are analyzed for the three most important and promising high-permittivity dielectrics, Al2O3, HfO2, and TiO2.

Nonlinear dynamics of the brain: emotion and cognition

Abstract: Experimental investigations of neural system functioning and brain activity are standardly based on the assumption that perceptions, emotions, and cognitive functions can be understood by analyzing steady-state neural processes and static tomographic snapshots. The new approaches discussed in this review are based on the analysis of transient processes and metastable states. Transient dynamics is characterized by two basic properties, structural stability and information sensitivity. The ideas and methods that we discuss provide an explanation for the occurrence of and successive transitions between metastable states observed in experiments, and offer new approaches to behavior analysis. Models of the emotional and cognitive functions of the brain are suggested. The mathematical object that represents the observed transient brain processes in the phase space of the model is a structurally stable heteroclinic channel. The possibility of using the suggested models to construct a quantitative theory of some emotional and cognitive functions is illustrated.

Metastability of current sheets

Abstract: Academy of Sciences (RAS), was held on 26 May 2010 at the conference hall of the Lebedev Physical Institute, RAS. The session was devoted to the 85th birthday of S I Syrovatskii. The program announced on the web page of the RAS Physical Sciences Division (www.gpad.ac.ru) contained the following reports: (1) Zelenyi L M (Space Research Institute, RAS, Moscow) ``Current sheets and reconnection in the geomagnetic tail''; (2) Frank A G (Prokhorov General Physics Institute, RAS, Moscow) ``Dynamics of current sheets as the cause of flare events in magnetized plasmas''; (3) Kuznetsov V D (Pushkov Institute of Terrestrial Magnetism, the Ionosphere, and Radio Wave Propagation, RAS, Troitsk, Moscow region) ``Space research on the Sun''; (4) Somov B V (Shternberg Astronomical Institute, Lomonosov Moscow State University, Moscow) ``Strong shock waves and extreme plasma states''; (5)Zybin K P (Lebedev Physical Institute, RAS,Moscow) ``Structure functions for developed turbulence''; (6) Ptuskin V S (Pushkov Institute of Terrestrial Magnetism, the Ionosphere, and Radio Wave Propagation, RAS, Troitsk, Moscow region) ``The origin of cosmic rays.'' Papers based on reports 1±4 and 6 are published in what follows.

Molecular energy transducers of the living cell. Proton ATP synthase: a rotating molecular motor

Abstract: The free energy released upon the enzymatic hydrolysis of adenosine triphosphate (ATP) is the main source of energy for the functioning of the living cell and all multicellular organisms. The overwhelming majority of ATP molecules are formed by proton ATP synthases, which are the smallest macromolecular electric motors in Nature. This paper reviews the modern concepts of the molecular structure and functioning of the proton ATP synthase, and real-time biophysical experiments on the rotation of the 'rotor' of this macromolecular motor. Some mathematical models describing the operation of this nanosized macromolecular machine are described.

Classification of Ge hut clusters in arrays formed by molecular beam epitaxy at low temperatures on the Si(001) surface

Abstract: Ge hut clusters forming quantum dot arrays on the Si(001) surface in the process of low-temperature ultrahigh-vacuum molecular beam epitaxy are morphologically investigated and classified using in situ scanning tunnelling microscopy. It is found that two main Ge hut cluster types—pyramidal and wedge-shaped—have different atomic structures, and it is concluded that shape transitions between the two are impossible. Derivative cluster species — obelisks (or truncated wedges) and accreted wedges — are revealed and investigated for the first time and shown to start dominating at high Ge coverages. The uniformity of cluster arrays is shown to be controlled by the scatter in the lengths of wedge-like clusters. At low growth temperatures (360 °C), cluster nucleation during the growth of the array is observed for all values of Ge coverage except for a particular point at which the arrays are more uniform than at higher or lower coverages. At higher temperatures (530 °C), no cluster nucleation is observed after the initial formation of the array.

Invisible cloaking of material bodies using the wave flow method

Abstract: The current knowledge of the physics of electromagnetic cloaking of material objects by the wave flow method is reviewed. Experiments demonstrating the feasibility of this cloaking method are described. Some aspects of calculating cloak profiles are examined, and achievements and unsolved problems in the theory of the interaction of electromagnetic waves with shells are considered. Prospects for developing the cloaking method for waves of other physical nature (acoustic and probability density waves) are discussed.

21st century: what is life from the perspective of physics?

Abstract: The evolution of the biophysical paradigm over 65 years since the publication in 1944 of Erwin Schrodinger's What is Life? The Physical Aspects of the Living Cell is reviewed. Based on the advances in molecular genetics, it is argued that all the features characteristic of living systems can also be found in nonliving ones. Ten paradoxes in logic and physics are analyzed that allow defining life in terms of a spatial–temporal hierarchy of structures and combinatory probabilistic logic. From the perspective of physics, life can be defined as resulting from a game involving interactions of matter one part of which acquires the ability to remember the success (or failure) probabilities from the previous rounds of the game, thereby increasing its chances for further survival in the next round. This part of matter is currently called living matter.

Spin superfluidity and magnons Bose–Einstein condensation

Abstract: The spin superfluidity -- superfluidity in the magnetic subsystem of a condensed matter - is manifested as the spontaneous phase-coherent precession of spins first discovered in 1984 in 3He-B. This superfluid current of spins - spin supercurrent - is one more representative of superfluid currents known or discussed in other systems, such as the superfluid current of mass and atoms in superfluid 4He; superfluid current of electric charge in superconductors; superfluid current of hypercharge in Standard Model of particle physics; superfluid baryonic current and current of chiral charge in quark matter; etc. Spin superfluidity can be described in terms of the Bose condensation of spin waves - magnons. We discuss different phases of magnon superfluidity, including those in magnetic trap; and signatures of magnons superfluidity: (i) spin supercurrent, which transports the magnetization on a macroscopic distance more than 1 cm long; (ii) spin current Josephson effect which shows interference between two condensates; (iii) spin current vortex - a topological defect which is an analog of a quantized vortex in superfluids, of an Abrikosov vortex in superconductors, and cosmic strings in relativistic theories; (iv) Goldstone modes related to the broken U(1) symmetry - phonons in the spin-superfluid magnon gas; etc. We also touch the topic of spin supercurrent in general including spin Hall and intrinsic quantum spin Hall effects.

Near-surface quantum states of neutrons in the gravitational and centrifugal potentials

Abstract: Two related physical phenomena have recently been observed: quantum states of ultracold neutrons (UCN) in the gravitational field above a flat mirror, and quantum states of cold neutrons (CN) in an effective centrifugal potential in the vicinity of a concave mirror. The two phenomena are similar in terms of their associated experimental methods and mathematical representations as well as in terms of their applications in particle physics, quantum optics, and surface physics.

The quark–gluon medium

Abstract: The properties of the quark–gluon medium observed in high-energy nucleus–nucleus collisions are discussed. The main experimental facts about these collisions are briefly described and compared with data about proton–proton collisions. Both microscopic and macroscopic approaches to their description are reviewed. The chromodynamics of the quark–gluon medium at high energies is mainly considered. The energy loss of partons moving in this medium is treated. The principal conclusion is that the medium possesses some collective properties which are crucial for understanding the experimental observations.

Large-radius bipolaron and the polaron-polaron interaction

Abstract: Research on the polaron–polaron interaction and the theory of large-radius bipolarons are reviewed. The difference between the two-center and one-center continuum bipolaron models in isotropic and anisotropic crystals is discussed. It is shown that the inclusion of electron–electron correlations can significantly reduce the bipolaron and D−-center energies as well as the energies of exchange-bound pairs of shallow hydrogen-like centers. The two-center bipolaron configuration corresponds to a shallow secondary minimum and is unstable. The phonon-mediated exchange interaction between Pekar polarons has an antiferromagnetic nature and exceeds the ferromagnetic interaction due to the Coulomb interaction of electrons localized in polaron potential wells. The possibility that the superfluidity of bipolarons can give rise to high-temperature superconductivity is discussed and problems related to the Wigner crystallization of a polaron gas are examined.

Experimental methods for determining the melting temperature and the heat of melting of clusters and nanoparticles

Abstract: Unlike macroscopic objects, clusters and nanoparticles lack a definite melting temperature at a given pressure but rather have their solid and liquid phases coexistent in a certain temperature range and their melting temperature dependent on the particle size. As the particle size decreases, the melting temperature becomes fundamentally difficult to define. This review examines methods for measuring the melting temperature and the heat of melting of clusters and nanoparticles. The temperature (internal energy) of the particles is defined and how it affects the properties of and processes involving the particles is discussed. The melting features of clusters and nanoparticles versus bulk materials are examined. Early methods of determining the melting temperature of large clusters are described. New precision methods of measuring the melting temperature and the heat of melting of clusters are discussed, which use the clusters themselves as 'high-sensitivity calorimeters' to measure energy. Laser-based nanoparticle melting techniques are outlined.

Submerged Landau jet: exact solutions, their meaning and application

Abstract: Exact hydrodynamic solutions generalizing the Landau submerged jet solution are reviewed. It is shown how exact inviscid solutions can be obtained and how boundary layer viscosity can be included by introducing parabolic coordinates. The use of exact solutions in applied hydrodynamics and acoustics is discussed. A historical perspective on the discovery of a class of exact solutions and on the analysis of their physical meaning is presented.

Dynamic compression of hydrogen isotopes at megabar pressures

Abstract: We review the results of shock compression of solid protium to the pressure 66 GPa, of liquid deuterium to 110 GPa, and of solid deuterium to 123 GPa in explosive devices of spherical geometry. The results are compared with data obtained by US scientists using traditional energy sources (explosives and light-gas guns), striker acceleration in a strong magnetic field (Z facility at Sandia), and powerful lasers (Nova at Lawrence Livermore National Laboratory (LLNL) and Omega at the Laboratory for Laser Energetics, University of Rochester). Results of density measurements of hydrogen isotopes under quasi-isentropic compression are analyzed. The absence of an anomalous increase in density under shock and quasi-isentropic compression of hydrogen isotopes is demonstrated. On the other hand, both processes exhibit a sharp change in the compression curve slopes, at the respective pressures 45 and 300 GPa.