[en] The use of muon probes in sold state physics and in particular for probing defect properties is discussed. The method involves the monitoring of the spin orientation, affected by local magnetic fields, of the muons decaying in the solids under investigation. The principle processes involved; the slowing-down process in which the muon loses energy and finally comes to rest, the diffusion process, defect trapping due to the strain fields of imperfections or to their perturbation of the electronic structure, and the limits imposed by the characteristic muon decay time, are considered. The four main temperature regimes involved in model trapping behaviour are examined. Prospects for muon studies in material physics are considered and the need to relate muon defect studies to standard techniques is suggested. (UK)

[en] The present status of slow positron beams for surface studies is reviewed briefly and examples given of new experiments which should be possible soon with the introduction of a new generation of positron beams with high flux and brightness. (author)

[en] The paper discusses the insulating spin density wave ground state, which occurs in many of the TMTSF family of organic superconductors. The magnetically ordered state associated with the metallic state in high magnetic fields, is also examined. (U.K.)

[en] The discovery of superconductivity in materials with an electronic effective mass of several hundred is stimulating considerable experimental and theoretical work. First, to clarify the nature of superconductivity - ie whether it arises from pairing of even or odd parity, the classification of states, their excitations and defect structures, and the nature of the electron-electron interaction effects leading to the pairing. And secondly to explain the physics behind the appearance at low temperatures of 4f and 5f related resonances as Fermi-liquids with huge masses, and their phase diagram at even lower temperatures, where they occur as superconductors of one or another variety, antiferro- or ferromagnets, or possibly remain as Fermi-liquids, as various different interaction effects compete. To introduce the principal theoretical issues, a brief introduction to valence fluctuations and heavy Fermion materials and their characteristic properties is given and then discussed qualitatively. (U.K.)

[en] Spectacular diamagnetic anomalies observed in CuCl samples under pressure have been the subject of intense investigation for the past few years. The reasons for the lack of definitive experiments which are needed to clarify the behaviour are discussed. A speculative model involving superconductivity at interfaces of micrometallic domains imbedded in dielectric is consistent with known facts but far from proven. 40 references. (author)

[en] The case for believing that the helium surface at a solid boundary has a two-dimensional spectrum of excitations and that these excitations are accessible for experimental study is examined. The physical picture which emerges from recent experiments, point to the existence of two-dimensional rotons which are accessible to measurement. These rotons are not associated with a constrained-geometry thin film but rather they characterize any liquid-solid interface bounding a volume of bulk helium. The evidence and its interpretation are explored. (U.K.)

[en] Illustrative examples of neutron scattering as a means of studying electronic properties of materials are discussed which include scattering by localized electrons, narrow-band materials and electron plasmas. Several examples of particular current interest including highly anisotropic band-electron states found in A-15 compounds and conducting polymers occur within this range of electron localization. (U.K.)

[en] The paper reviews valence fluctuation and heavy fermion materials, and their superconductivity. The subject is discussed under the various topic headings: the regimes of the physics of rare-earth and actinide compounds, theories for confined moment and fluctuating valence, superconductivity in heavy fermions, conventional or unconventional superconductivity, characterization of superconducting states, experiments identifying type of superconducting state, tunneling, impurities, and critical fields. (U.K.)