Quench dynamics and gap oscillations of non-equilibrium multiband superconductors*

Superconductors driven to non-equilibrium steady states display the remarkable phenomenon of coherent gap oscillations. With the rapid advances in THz pump-and-probe techniques, this concept has been widely explored both theoretically and experimentally. In several superconductors of general interest, such as SrTiO₃, iron pnictides, Sr₂RuO₄, and heavy fermions, multiple bands cross the Fermi level, giving rise to multiband superconductivity. Here, we combine analytical and numerical methods to solve the time-dependent multiband BCS equations and investigate the gap oscillations in quenched multiband superconductors. We find the existence of multiple oscillation frequencies, which can promote beating of the gap oscillations. Interestingly, we find that the oscillations decay faster than in the one band case, with a power-law of 1/t^3/2 instead of 1/t^1/2. We explore a variety of different parameter regimes and discuss the relevance of our results to experiments.