Higgs amplification in non-equilibrium K3C60

The quest for new functionalities in quantum materials has recently been extended to non-equilibrium states. In the context of superconductivity, examples have included the generation of  transient superconductivity above the thermodynamic transition temperature, the excitation of coherent Higgs-mode oscillations, and the optical control of the interlayer phase in the cuprates.  In this talk, I will propose that a prompt quench into a transient superconducting state from a metal induces large Higgs fluctuations of the order parameter, and will demonstrate that these fluctuations give rise to the amplification of light at frequencies below the superconducting gap. I will show new measurements on K3C60, in which these predictions are verified experimentally.