EFFECT OF THERMAL FLUCTUATIONS ON LONG-RANGE ORDER IN TYPE-II SUPERCONDUCTORS

Different definitions of the phase PHI(gi)(r) of the gauage-invariant order parameter in type-II superconductors re compared. It is shown that all phases satysfy the same equations and the boundary conditions. In a mixed state the multi-valued part of PHI(gi)(r) makes a dominant contribution to the correlation function of the order parameter and leads to an off-diagonal long-range order destruction by thermal fluctuations for three-dimensional superconductors. Possible consequences of long-range order destruction are discussed for type-II superconductors in magnetic field.