Type II superconductors

A review is given of recent work which has led to the discovery of type II superconductors and to an understanding of many of their properties. A brief historical introduction, which summarizes the early ideas concerning the magnetic behaviour of superconductors, is followed by a presentation of the Ginzburg-Landau equations. Some of the more general consequences of these equations, including the existence of quantized vortex lines, are examined. Abrikosov's solutions of the Ginzburg-Landau equations in homogeneous, extended defect-free, bulk specimens of type II superconductors are then presented, and the more recent work which generalizes the theory to all temperatures is mentioned. These predictions are then compared with measurements of the bulk thermodynamic properties and with various experiments which confirm the existence of vortex lines. Two special effects, the superconducting surface sheath and the influence of the paramagnetism of the normal state, are then discussed. The article concludes with a section devoted to irreversible phenomena. Particular attention is paid (i) to vortex line pinning, the static irreversible magnetic behaviour and bulk transport currents, and (ii) to the various types of vortex line motion: flux creep, flux flow, vortex line vibrations and flux jumps.