Control of Non-equilibrium Quantum Phases and Collective Modes in Superconductors by Terahertz Light-Driven Supercurrents

In superconductors several non-equilibrium phases exist ranging from quenched states to gapless superconducting phases with gapless excitation spectrum but unchanged macroscopic coherence and infinite conductivity. The dynamics of such non-equilibrium phases is associated with observation of collective modes which provide details about the underlying nature of superconductivity. Although recent advances in THz laser spectroscopy make the excitation of collective modes and gapless superconducting phases possible, their observations in ultrafast spectroscopy remain challenging. Here we demonstrate control of the non-equilibrium dynamics in superconductors by THz light-driven supercurrents. By applying a microscopic gauge-invariant theory we show that selective non-equilibrium phases can be excited and amplitude Higgs mode can be detected in the nonlinear response by inducing supercurrents via THz pulse shaping. THz light-control of supercurrents also allows for generation of a comb of odd or odd and even harmonics in emission.