Higgs Spectroscopy of Superconductors in Nonequilibrium

Abstract

The collective non-equilibrium dynamics of superconducting condensates could not be studied systematically so far. The response in conventional optical pump-probe experiments contains almost no information on the actual ground state, since it is limited to high-energy processes. Recent development of pulsed THz laser technology has made it possible to excite superconducting Higgs oscillations, without melting the superconducting order. Here we develop a theory for tailored quantum quenches which can excite all possible symmetries of Higgs oscillations. In analogy to phonon spectroscopy, these oscillations allow for a complete characterization of the superconducting gap function. Simulations for realistic laser pulses reveal spectroscopic information of these Higgs oscillations in the optical conductivity. By exemplary calculating the nonequilibrium response of s- and d-wave superconductors we show, that such nonequilibrium Higgs spectroscopy opens a unique approach to distinguish between different symmetries of the condensate, even for new and unknown superconductors.