Superconductivity and electronic properties of layered compounds

The electrical, optical, and magnetic properties of layered compounds of dichalcogenides of transition metals and intercalated crystals are considered. Particular attention is paid to the anisotropy of these properties and to the analysis of the changes produced by intercalation. Experimental data are presented on the structural transitions in layered crystals and are examined from the point of view of the ideas concerning the charge-density wave. The bulk of the review is devoted to the superconducting properties of layered compounds (the critical temperature, the specific-heat discontinuity in the transition, the gap, the fluctuations above Tc, and the magnetic properties of ordinary and intercalated layered superconductors). The theoretical concepts that make it possible to describe the distinguishing features of the superconducting properties of layered and intercalated compounds are discussed (the effective-mass model and the model of Josephson interaction between layers).