High-$T_c$ superconductors from the experimental point of view

An analysis is made of experimental data from measurements of the specific heat, the resistivity, the critical magnetic fields, the paramagnetic susceptibility above $T_c$, the Hall effect, and of other properties of the two new types of superconducting materials: lanthanum cuprates and the 1-2-3 compounds. The results of this analysis are discussed from the point of view of applying the Fermi-liquid picture to the description of the normal and superconducting properties of these materials, the role of fluctuations near the critical temperature, and the dimensionality of the superconductivity in them. Estimates of the width of the conduction band and of some other microscopic parameters indicate that there is a rather wide (about 0.7 eV) delocalized band. The fluctuations region near $T_c$ is narrow, but nonetheless wider than that in ordinary superconductors. The superconductivity near $T_c$ is three-dimensional, although sufficiently far from $T_c$ the layered nature of the structure may be important.