We study the nonlinear optical response in a superconducting NbN thin film with strong terahertz (THz)wave. Besides the expected third harmonic generation, we observe a new transient oscillation which softensin frequency with temperature increasing towards superconducting transition temperatureTc. We identify thisnew mode as the Higgs transient oscillation. To verify this proposal, we introduce a time-frequency resolvedtechnique, named spectrogram for visualizing THz spectrum. The dynamic decaying behavior of the mode isobserved, which is consistent with theoretical expectation about intrinsic Higgs oscillation. Moreover, a higherorder nonlinear optics effect,i.e.fifth harmonic generation, has been observed for the first time, which we assignto the higher order coupling between Higgs mode and electromagn
@article{arxiv.2107.07488,
title = {Transient Higgs oscillations and high-order nonlinear light-Higgs coupling in terahertz-wave drivenNbN superconductor},
author = {Z. X. Wang and J. R. Xue and H. K. Shi and X. Q. Jia and T. Lin and L. Y. Shi and T. Dong and F. Wang and N. L. Wang},
journal= {arXiv preprint arXiv:2107.07488},
year = {2022}
}