Electromagnetic response of a vortex in layered superconductors

We calculate the response of a vortex core in a layered superconductor to an ac electromagnetic field. In particular we investigate the intermediate clean regime, where the broadening of the vortex core bound states is comparable to or larger than the level spacing. The response of the order parameter, impurity self-energy, and currents are obtained by a self-consistent determination of the distribution functions and the excitation spectrum. The response is dominated by order parameter collective modes coupled to the fermion excitations of the vortex core. At low frequencies this coupling leads to substantially enhanced absorption in the vortex core.