Ultrafast nonthermal terahertz electrodynamics and possible quantum energy transfer in the Nb3Sn superconductor

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2019-03-07
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Yang, Xu
Zhao, X.
Vaswani, Chirag
Sundahl, C.
Song, Boqun
Yao, Yong-Xin
Cheng, Di
Liu, Zhiyan
Orth, Peter
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Orth, Peter
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Physics and Astronomy
Physics and astronomy are basic natural sciences which attempt to describe and provide an understanding of both our world and our universe. Physics serves as the underpinning of many different disciplines including the other natural sciences and technological areas.
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Ames National LaboratoryPhysics and Astronomy
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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 ℏω absorption to create QPs set by 2ΔSC/ℏω=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.

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