Far-infrared electrodynamics of thin superconducting NbN film in magnetic fields

We studied a thin superconducting NbN film in magnetic fields up to 8 T above the zero-temperature limit by means of time-domain terahertz and scanning tunneling spectroscopies in order to understand the vortex response. Scanning tunneling spectroscopy was used to determine the optical gap and the upper critical field of the sample. The values obtained were subsequently used to fit the terahertz complex conductivity spectra in the magnetic field in the Faraday geometry above the zero-temperature limit. These spectra are best described in terms of the Coffey-Clem self-consistent solution of a modified London equation in the flux creep regime.