title: Transient increase of the energy gap of superconducting NbN thin films excited by resonant narrow-band terahertz pulses.
abstract: Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2Δ/h. Utilizing intense, narrow-band, picosecond, terahertz pulses, tuned to just below and above 2Δ/h of a BCS superconductor NbN, we demonstrate that the superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced nonthermal electron distribution persisting on a 100 ps time scale.
authors.affiliation: Department of Physics and Center for Applied Photonics, University of Konstanz, D-78457, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Beck
authors.forename: I
authors.initials: I
authors.lastname: Rousseau
authors.forename: M
authors.initials: M
authors.lastname: Klammer
authors.forename: P
authors.initials: P
authors.lastname: Leiderer
authors.forename: M
authors.initials: M
authors.lastname: Mittendorff
authors.forename: S
authors.initials: S
authors.lastname: Winnerl
authors.forename: M
authors.initials: M
authors.lastname: Helm
authors.forename: G N
authors.initials: GN
authors.lastname: Gol'tsman
authors.forename: J
authors.initials: J
authors.lastname: Demsar