Abstract: Far-infrared techniques played a crucial role in the
experimental validation of Bardeen–Cooper–Schrieffer (BCS) theory and
they continue to provide fundamental information about condensate,
quasiparticle and vortex behaviour in both equilibrium and
non-equilibrium states of superconductors.
In this talk, we will focus on the response of thin superconducting
NbN films. We confirmed that their equilibrium conductivity follows the
conventional BCS theory. Application of a dc magnetic field induces
vortices in the films, which leads to qualitatively different responses,...