Showing papers in "Advances in Physics in 1999"

Mixed-valence manganites

Abstract: Mixed-valence manganese oxides (R1-χAχ)MnO3 (R=rare-earth cation, A=alkali or alkaline earth cation), with a structure similar to that of perovskite CaTiO3, exhibit a rich variety of crystallographic, electronic and magnetic phases. Historically they led to the formulation of new physical concepts such as double exchange and the Jahn-Teller polaron. More recent work on thin films has revealed new phenomena, including colossal magnetoresistance near the Curie temperature, dense granular magnetoresistance and optically-induced magnetic phase transitions. This review gives an account of the literature on mixed-valence manganites, placing new results in the context of established knowledge of these materials, and other magnetic semiconductors. Issues addressed include the nature of the electronic ground states, the metal-insulator transition as a function of temperature, pressure and applied magnetic field, the electronic transport mechanisms, dielectric and magnetic polaron formation, magnetic localization, ...

Fullerenes under high pressures

Abstract: This Chapter deals with the structures and physical properties of solid fullerenes under high pressures. Subjects discussed include the interaction between fullerenes and pressure media, the phase ...

Local magnetic probes of superconductors

Abstract: Investigations of the magnetic properties of high temperature superconductors (HTSs) have revealed the existence of striking new vortex phenomena due, in part, to their strong crystalline anisotropy, very short coherence lengths and the much larger thermal energies available at high temperatures Some of these phenomena, for example vortex lattice 'melting', pose serious problems for technological applications of the most anisotropic HTS materials and a fuller understanding of them is of considerable importance The most direct information regarding vortex structures and dynamics is obtained through local measurement of the magnetic field within or at the surface of a superconducting sample A detailed review of such local magnetic probes is presented here including Lorentz microscopy, magnetic force microscopy, Bitter decoration, scanning Hall probe microscopy, magneto-optical imaging, and scanning superconducting quantum interference device microscopy In each case the principles underpinning the techni

Curvature elasticity of thin films

Abstract: A tutorial review of the theory of curvature elasticity of thin films is presented with an emphasis on the physical origins of the bending energy We begin with a discussion of surface curvature and focus on the role of special surfaces of curvature to show how such surfaces can be defined to eliminate either the coupling of the compressibility and bending terms (neutral surface) or the saddle-splay (Gaussian curvature) modulus Next, we consider phenomenological models for curvature elasticity and discuss the coupling of the curvature degrees of freedom with other properties of the system such as the packing area and the number of molecules at the interface The pressure distribution in the film is related to the bending moduli We then connect the elastic moduli to the physical properties of both solid and liquid thin films with a detailed discussion of the role of solid elasticity (including defects), electrostatic interactions (applicable to polar head groups and chain packing (using a block copolymer

Magnetism of actinide compounds

Abstract: We review the physical properties of actinide compounds, with particular emphasis on their magnetic characteristics. Because of the complexity of these materials, mainly the simplest compounds are treated, some of which have properties that can be theoretically explained.

The role of density of states fluctuations in the normal state properties of high Tc superconductors

Abstract: During the last decade a lot of efforts have been undertaken to explain the unusual normal state properties of high temperature superconductors (HTS) in the framework of unconventional theories based on strongly interacting electrons, pre-formed Cooper pairs, polaron mechanism of super conductivity etc. A different approach to this problem would be to develop the perturbation theory for interacting electrons in the normal phase of strongly anisotropic superconductors without specifying the origin of this interaction. The Cooper channel of interelectron interaction is equivalent to the superconducting fluctuations which are unusually strong in HTS. We show that the peculiarities of such systems not only lead to the increase of the magnitude but are also frequently responsible for the change of the hierarchy of different fluctuation effects and even of the sign of the total corrections. As a result the fluctuation contributions can manifest themselves in very unusual forms. The first and well known result i...

Quantum-coherent transport of a heavy particle in a fermionic bath

Abstract: In this review, a detailed discussion of the behaviour of a heavy particle interacting with a Fermi sea is given. Particular emphasis is put on the issue of how strong correlations influence coherence and transport of the particle. First, we investigate the question of whether the heavy particle is a well defined quasiparticle at low temperatures. While in one dimension ( D = 1) and at a van Hove singularity in D = 2 the coherence of the particle is destroyed, the quasiparticle weight is finite in higher dimensions. The most important transport quantity is the diffusion constant or mobility of the heavy particle. We are able to describe both the well known high-temperature properties and the cross-over to the lowest temperatures in a unified approximation scheme based on a self-consistent evaluation of an effective action. Two strong-correlation effects of independent origin are discussed. The first arises if the scattering of the fermions from the heavy particle is nearly resonant, that is, if one of the...

Inversion of low-energy electron diffraction data with no pre-knowledge factor beyond optical holography

Abstract: In this review, I describe how low-energy (typically below 500eV) electron diffraction spectra can be inverted to produce three-dimensional coordinates of atoms neighbouring a reference atom with no prior knowledge of what type or types of atom are present. The reference atom may be one of many equivalent near-surface atoms from which a core-level photoelectron is excited or, in the case of diffuse low-energy electron diffraction, one of many equivalent adsorbate atoms (lacking in long-range order) on the surface of a crystalline substrate. Other variants apply to low-energy electron diffraction, Kikuchi electron diffraction and time-reversed versions in which the wavenumber (energy) and direction of the incident beam are varied. I show that, for such low-energy electron diffraction spectra, the relative phases between the reference wave and scattered waves have a known geometric form if the spectra are taken from within a small angular cone in the near-back-scattering directions. By using the back-scatte...

Aspects of criterion validity and sensitivity of the BAS-health scale in chronic pain patients - a pilot study of patients at a multidisciplinary pain centre.

Abstract: Aspects of criterion validity and sensitivity of the BAS-health scale in chronic pain patients - a pilot study of patients at a multidisciplinary pain centre.