Critical fluctuations in strongly type-II quasi-two-dimensional superconductors

The critical fluctuations near ${\mathit{H}}_{\mathit{c}2}$(T) in the mixed phase of layered type-II superconductors are related to an equivalent system of classical particles with many-body ‘‘gauge’’ interactions. The scale invariance of this dense vortex plasma leads to a universal character of the vortex solid-liquid melting line where the transition to the superconducting state occurs. The relation to experimental situation in high-${\mathit{T}}_{\mathit{c}}$ and other layered superconductors and superconducting thin films is discussed.