Showing papers in "Advances in Physics in 2005"
TL;DR: In this paper, a band of physicists gathered for five weeks at the Aspen Center for Physics to discuss the pseudogap at high temperature cuprate superconductivity, and discussed the importance of this phase in the context of strongly correlated electron systems.
Abstract: Although nineteen years have passed since the discovery of high temperature cuprate superconductivity 1, there is still no consensus on its physical origin. This is in large part because of a lack of understanding of the state of matter out of which the superconductivity arises. In optimally and underdoped materials, this state exhibits a pseudogap at temperatures large compared to the superconducting transition temperature 2, 3. Although discovered only three years after the pioneering work of Bednorz and Muller, the physical origin of this pseudogap behavior and whether it constitutes a distinct phase of matter is still shrouded in mystery. In the summer of 2004, a band of physicists gathered for five weeks at the Aspen Center for Physics to discuss the pseudogap. In this perspective, we would like to summarize some of the results presented there and discuss the importance of the pseudogap phase in the context of strongly correlated electron systems. Contents PAGE Acknowledgments730References730
464 citations
TL;DR: The physics of granular materials in ambient gases is governed by interparticle forces, gas-particle interaction, geometry of particle positions and geometry of particles contacts as mentioned in this paper, which are strongly dependent on the external forces, boundary conditions and on the assembling procedure.
Abstract: Memento, homo, qui pulvis est et pulverem reverteris. Genesis 3 Polvos seran, mas polvo enamorado. Francisco de Quevedo The physics of granular materials in ambient gases is governed by interparticle forces, gas–particle interaction, geometry of particle positions and geometry of particle contacts. At low consolidations these are strongly dependent on the external forces, boundary conditions and on the assembling procedure. For dry fine powders of micron and sub-micron particle size interparticle attractive forces are typically much higher than particle weight, and particles tend to aggregate. Because of this, cohesive powders fracture before breaking, flow and avalanche in coherent blocks much larger than the particle size. Similarly the drag force for micron sized particles is large compared to their weight for velocities as low as 1 mm/s. Due to this extreme sensitivity to interstitial gas flow, powders transit directly from plastic dense flows to fluidization without passing through collisional re...
450 citations
TL;DR: In this paper, it is demonstrated that although wet granular systems are quite complex, their main features may be understood on the basis of rather simple concepts, such as statistical concepts, dynamics, and phase transitions.
Abstract: Recent advances in understanding model systems of wet granular materials are presented, with particular emphasis on statistical concepts, dynamics, and phase transitions. It is demonstrated that although wet granular systems are quite complex, their main features may be understood on the basis of rather simple concepts. The significance of these systems for investigating fundamental problems of non-equilibrium dynamics are shortly discussed.
349 citations
TL;DR: In this article, the authors described a new class of phenomena based on the interaction between spatially separated, but closely located ferromagnets and superconductors, the so-called ferromagnet-superconductor hybrids (FSH).
Abstract: The new class of phenomena described in this review is based on the interaction between spatially separated, but closely located ferromagnets and superconductors, the so-called ferromagnet–superconductor hybrids (FSH). Typical FSH are: coupled uniform and textured ferromagnetic and superconducting films, magnetic dots over a superconducting film, magnetic nanowires in a superconducting matrix, etc. The interaction is provided by the magnetic field generated by magnetic textures and supercurrents. The magnetic flux from magnetic structures or topological defects can pin vortices or create them, changing the transport properties and transition temperature of the superconductor. On the other hand, the magnetic field from supercurrents (vortices) strongly interacts with the magnetic subsystem, leading to formation of coupled magnetic–superconducting topological defects. Each time the Nambu and spin matrices are written together we mean the direct product. The proximity of ferromagnetic layer dramatically cha...
309 citations
TL;DR: In this article, the authors studied the dynamics of complex condensed materials at a wide range of different time scales, which complicates the study of such processes with computer simulations and is a challenge for the computer simulator who wants to study such processes.
Abstract: Often, the dynamics of complex condensed materials is characterized by the presence of a wide range of different time scales, complicating the study of such processes with computer simulations Consider, for instance, dynamical processes occurring in liquid water Here, the fastest molecular processes are intramolecular vibrations with periods in the 10–20 fs range The translational and rotational motions of water molecules occur on a significantly longer time scale Typically, the direction of translational motion of a molecule persist for about 500 fs, corresponding to 50 vibrational periods Hydrogen bonds, responsible for many of the unique properties of liquid water, have an average lifetime of about 1 ps and the rotational motion of water molecules stays correlated for about 10 ps Much longer time scales are typically involved if covalent bonds are broken and formed For instance, the average lifetime of a water molecule in liquid water before it dissociates and forms hydroxide and hydronium ions is on the order of 10 h This enormous range of time scales, spanning nearly 20 orders of magnitude, is a challenge for the computer simulator who wants to study such processes
289 citations
TL;DR: A review of recent developments in the theoretical, numerical and experimental study of slow dynamics in colloidal systems, with a particular emphasis on the glass transition phenomenon, can be found in this paper.
Abstract: This review focuses on recent developments in the theoretical, numerical and experimental study of slow dynamics in colloidal systems, with a particular emphasis on the glass transition phenomenon. Colloidal systems appear to be particularly suited for tackling the general problem of dynamic arrest, since they show a larger flexibility compared to atomic and molecular glasses because of their size and the possibility of manipulating the physical and chemical properties of the samples. Indeed, a wealth of new effects, not easily observable in molecular liquids, have been predicted and measured in colloidal systems. The slow dynamic behavior of three classes of colloidal suspension is reviewed – hard colloids, short-range attractive colloids and soft colloidal systems – selecting the model systems among the most prominent candidates for grasping the essential features of dynamic arrest. Emphasis is on the possibility of performing a detailed comparison between experimental data and theoretical predictions b...
235 citations
TL;DR: In this article, a review of single-particle momentum distributions in light atoms and molecules is presented with specific emphasis on experimental measurements using the deep inelastic neutron scattering technique at eV energies.
Abstract: Studies of single-particle momentum distributions in light atoms and molecules are reviewed with specific emphasis on experimental measurements using the deep inelastic neutron scattering technique at eV energies. The technique has undergone a remarkable development since the mid-1980s, when intense fluxes of epithermal neutrons were made available from pulsed neutron sources. These types of measurements provide a probe of the short-time dynamics of the recoiling atoms or molecules as well as information on the local structure of the materials. The paper introduces both the theoretical framework for the interpretation of deep inelastic neutron scattering experiments and thoroughly illustrates the physical principles underlying the impulse approximation from light atoms and molecules. The most relevant experimental studies performed on a variety of condensed matter systems in the last 20 years are reviewed. The experimental technique is critically presented in the context of a full list of published work. ...
215 citations
TL;DR: A review of spin-polarized magnetic domain walls can be found in this article, where the authors discuss a variety of different physical effects, most notably a contribution to the electrical resistance caused by the wall, and a motion of the wall driven by the spinpolarised current.
Abstract: Electrical currents flowing in ferromagnetic materials are spin-polarised as a result of the spin-dependent band structure. When the spatial direction of the polarisation changes, in a domain structure, the electrons must somehow accommodate the necessary change in direction of their spin angular momentum as they pass through the wall. Reflection, scattering, or a transfer of angular momentum onto the lattice are all possible outcomes, depending on the circumstances. This gives rise to a variety of different physical effects, most importantly a contribution to the electrical resistance caused by the wall, and a motion of the wall driven by the spin-polarised current. Historical and recent research on these topics is reviewed. Contents PAGE 1. Introduction5862. Spin-polarised current587 2.1. Tunnelling current spin polarisation589 2.2. Ballistic current spin polarisation592 2.3. Diffusive current spin polarisation5933. Magnetic Domain Walls598 3.1. Basics of domain walls598 3.1.1. Domain wall thickness and...
206 citations
TL;DR: A review of the structural and magnetic properties of ultrathin epitaxial Fe films on GaAs(001) and related semiconductor substrates is presented in this article, where the authors try to settle some of these controversial issues, hence providing a long overdue common denominator for research in this area.
Abstract: This article presents a review of the structural and magnetic properties of ultrathin epitaxial Fe films on GaAs(001) and related semiconductor substrates. Interest in these systems and Fe/GaAs(001) in particular has increased significantly over the last two decades, largely due to the emergence of the field of magnetoelectronics. Since then numerous studies of molecular beam epitaxy of Fe on GaAs(001) have been carried out, making it by far the best researched Fe/semiconductor(001) system. Issues such as magnetic anisotropy in the ultrathin regime, however, remain controversial with contradictory reports in the literature giving rise to considerable controversy within the field. By carefully scrutinizing the enormous amount of literature published on Fe/GaAs(001) so far and analysing these results within the wider context of Fe/semiconductor(001) systems, this article tries to settle some of these controversial issues, hence providing a long overdue ‘common denominator' for research in this area.
158 citations
TL;DR: In this article, a large number of multifaceted quantum transport processes in molecular systems and physical nanosystems, such as nonadiabatic electron transfer in proteins, are treated in terms of quantum relaxation processes which couple to one or several fluctuating environments.
Abstract: A large number of multifaceted quantum transport processes in molecular systems and physical nanosystems, such as e.g. nonadiabatic electron transfer in proteins, can be treated in terms of quantum relaxation processes which couple to one or several fluctuating environments. A thermal equilibrium environment can conveniently be modelled by a thermal bath of harmonic oscillators. An archetype situation provides a two-state dissipative quantum dynamics, commonly known under the label of a spin-boson dynamics. An interesting and nontrivial physical situation emerges, however, when the quantum dynamics evolves far away from thermal equilibrium. This occurs, for example, when a charge transferring medium possesses nonequilibrium degrees of freedom, or when a strong time-dependent control field is applied externally. Accordingly, certain parameters of underlying quantum subsystem acquire stochastic character. This may occur, for example, for the tunnelling coupling between the donor and acceptor states of the t...
67 citations
TL;DR: In contrast to ferromagnets, in antiferromagnetic order, a large variety of magnetic structures can be stabilized at different temperatures and magnetic fields as discussed by the authors, which allows one to separate and distinguish the different mechanisms of magnetostriction.
Abstract: Magnetostriction in systems with rare-earth elements is a very general topic of interest because it characterizes the electronic magnetism of compounds as well as the interaction of the magnetic and the lattice system. The magnetostrictive behaviour of classical ferromagnets is widely investigated. The interpretation of the data is based on domain dynamics, crystal field effects and other magnetoelastic mechanisms, which are extremely difficult to separate. Therefore, in the last few years there has been great activity in the area of magnetostriction of antiferromagnets. In contrast to ferromagnets, in antiferromagnets a large variety of magnetic structures can be stabilized at different temperatures and magnetic fields. This fundamental property of antiferromagnets allows one to separate and distinguish the different mechanisms of magnetostriction. New classes of magnetic compounds with antiferromagnetic order, for example the borocarbides and some special manganites, have also focused research efforts o...