VORTEX FLUCTUATIONS IN LAYERED SUPERCONDUCTORS AND THIN-FILMS

We determine the free energy of a vortex fine within the Ginzburg-Land au formalism. Besides the usual translational modes we also take accou nt of self-fluctuations of the order parameter in the calculation of t he vortex free energy. The latter are due to the internal structure of a vortex line and lead to an observable downward renormalization of t he lower critical-field line H(c1) (T) in strongly layered superconduc tors. In thin films the self-fluctuations of the vortex lead to a redu ction in the power-law exponent of the current-voltage characteristic. We argue that in a three-dimensional system the spontaneous creation of vortex lines cannot occur.