Superconductivity and localization of electrons in disordered two-dimensional metal systems

A review is given of experimental and theoretical studies of changes in the superconducting properties of disordered two-dimensional metal systems as the metal-insulator transition is approached. Particular attention is devoted to ultrathin (including discontinuous and island) and granular films. The influence of disorder on the critical point T$_c$, the fluctuation conductivity above T$_c$, and the magnitude and temperature dependence of the upper critical field H$_{c2}$ are discussed. The effects of film inhomogeneity and the associated percolation effects on superconductivity are examined in some detail. Mechanisms responsible for quasireentrant phenomena associated with the establishment of phase coherence of electrons in inhomogeneous systems are extensively discussed.