SUPERCONDUCTING LONG-RANGE ORDER IN MIXED-STATE

It is shown that the controversies between different definitions of the gauge-invariant order parameter phase can be removed by taking into account that in the Meissner state transverse component A is gauge-invariant quantity and under gauge transformation only longitudinal component A changes. As a consequence, gauge-invariant order parameter phase and the phase within London gauge satisfy the same equations and boundary condition. For three dimensional superconductors in the mixed state it is shown that the destruction of superconducting long-range order parameter by thermal fluctuations does not depend on the definition of the order parameter.