Third harmonic generation from collective modes in disordered superconductors

Abstract

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 in ordinary spectroscopy. From the theoretical point of view, disorder effects must be included. Here, the authors show that by treating disorder nonperturbatively the THG is strongly enhanced by disorder, and phase and charge fluctuations, neglected so far, give a substantial contribution to it. In addition, the computed polarization dependence of the signal within realistic band structures challenges the interpretation of recent experiments in cuprates.