Restoration of the continuous phase transition in the vortex state due to lattice translational symmetry: Large-Nlimit

The critical behavior of type-II superconductors near the upper critical magnetic field ${\mathit{H}}_{\mathit{c}2}$(T) is studied. The thermal fluctuations are shown to forbid a spontaneous breakdown of the U(1) symmetry in d<4 dimensions within the 1/N expansion, where N is the complex order parameter component number. The lattice effects such as Harper’s broadening and splitting of Landau levels are found to restore the continuous phase transition in the conventional mixed state described by critical exponents which are identical to those of the Ginzburg-Landau model with H=0.