Fluctuations near superconducting phase transitions

Abstract

The effects of thermodynamic fluctuations near superconducting phase transitions are reviewed. Above T_c, fluctuations towards the superconducting state lead to the appearance of excess conductivity, diamagnetism, specific heat, and tunnelling currents. Below T_c, fluctuations towards the normal state lead to the appearance of resistance in thin wires and the breakdown of fluxoid quantization in small rings. These effects are generally small, but they can be measured experimentally, particularly in superconducting samples of reduced dimensionality (on the scale of the Ginzburg-Landau coherence length) such as thin films, whisker crystals, and powders. These phenomena are explained using Ginzburg-Landau theory (the salient features of which are developed concurrently), and the current status of theoretical and experimental studies of these effects is surveyed.