  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 obtained values 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.
