Transient Higgs modes in time-reversal-symmetry-breaking BCS superconductors

We study the transient dynamics of superconductors initially prepared at time-reversal-symmetry(T)-breaking states and assume the post-pump system evolves with a BCS Hamiltonian that preserves T. Such scenarios could occur in pump-probe experiments on superconductors, where the initial pump fields, such as circularly polarized laser lights, break T of the superconductors. Two types of T-breaking initial states are discussed: Zeeman splitting (h) of the fermion dispersions and complex superconducting order parameters ($\Delta_x+i\Delta_y$). We found that h can induce a transient Higgs mode, while $\Delta_y$ determines how the frequency of the Higgs mode deviates from $\Delta_\infty$. Finally, we discuss how such modes could be observed in time- and angle-resolved photoemission spectroscopy.