Observation of Higgs Amplitude Mode in s-wave Superconductors Induced by Nonadiabatic Terahertz Pulse Excitation(Research)

Abstract

By using the intense THz pump-THz probe spectroscopy, we observed the collective Higgs amplitude mode of the s-wave BCS order parameter in nonadiabatically-excited superconducting Nb_<1-x>Ti_xN films. The oscillation frequency is in good agreement with the asymptotic value of the BCS gap energy, indicating the appearance of the coherent oscillation of the order parameter amplitude. The result opens a new avenue to the ultrafast manipulation of the superconducting order parameter driven by a strong AC field.