Ultrafast Nonthermal Terahertz Electrodynamics And Possible Quantum Energy Transfer In The Nb3sn Superconductor

We report terahertz (THz) electrodynamics of a moderately clean A15 superconductor (SC) following ultrafast excitation to manipulate quasiparticle (QP) transport. In the Martensitic normal state, we observe a photo enhancement in the THz conductivity using optical pulses, while the opposite is observed for the THz pump. This demonstrates wavelength-selective nonthermal control of conductivity distinct from sample heating. The photo enhancement persists up to an additional critical temperature, above the SC one, from a competing electronic order. In the SC state, the fluence dependence of pair-breaking kinetics together with an analytic model provides an implication for a "one photon to one Cooper pair" nonresonant energy transfer during the 35-fs laser pulse; i.e., the fitted photon energy (sic)omega absorption to create QPs set by 2 Delta(SC)/(sic)omega = 0.33%. This is more than one order of magnitude smaller than in previously studied BCS SCs, which we attribute to strong electron-phonon coupling and possible influence of phonon condensation.