Transient increase of the energy gap in superconducting NbN thin Films excited by resonant narrow-band terahertz pulses


Transient increase of the energy gap in superconducting NbN thin Films excited by resonant narrow-band terahertz pulses

Beck, M.; Rousseau, I.; Klammer, M.; Leiderer, P.; Mittendorff, M.; Winnerl, S.; Helm, M.; Gol’tsman, G. N.; Demsar, J.

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, narrowband picosecond THz pulses, tuned to just below and above 2Δ=h of a BCS superconductor NbN, we demonstrate that 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 non-thermal electron distribution persisting on a 100 ps timescale.

Keywords: radiation-enhanced superconductivity; NbN; Time resolved spectroscopy

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Publ.-Id: 18896