Third harmonic generation from collective modes in disordered superconductors

The observation of third-harmonic generation (THG) in superconductors suggests that strong terahertz fields provide a preferential tool to excite collective excitations, e.g., the Higgs mode, which remain elusive ordinary spectroscopy. From theoretical point view, disorder effects must be included. Here, authors show by treating nonperturbatively THG is strongly enhanced disorder, and phase charge fluctuations, neglected so far, give substantial contribution it. In addition, computed polarization dependence signal within realistic band structures challenges interpretation recent experiments cuprates.