Vortex fluctuations in layered superconductors and thin films

We determine the free energy of a vortex line within the Ginzburg-Landau formalism. Besides the usual translational modes we also take account of self-fluctuations of the order parameter in the calculation of the vortex free energy. The latter are due to the internal structure of a vortex line and lead to an observable downward renormalization of the lower critical-field line ${\mathit{H}}_{\mathit{c}1}$(T) in strongly layered superconductors. In thin films the self-fluctuations of the vortex lead to a reduction 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.