Collective modes in pumped unconventional superconductors with competing ground states

Motivated by the recent development of terahertz pump-probe experiments, we investigate the short-time dynamics in superconductors with multiple attractive pairing channels and competing nematic order. Studying a single-band and multiband superconductors, we find the signatures of collective excitations of the pairing symmetries (known as Bardasis-Schrieffer modes) as well as the order parameter amplitude (Higgs mode) in the short-time dynamics of the spectral gap and quasiparticle distribution after an excitation by a pump pulse. We show that the polarization and intensity of the pulse can be used to control the symmetry of the non-equilibrium state as well as frequencies and relative intensities of the contributions of different collective modes. We find particularly strong signatures of the Bardasis-Schrieffer mode in the dynamics of the quasiparticle distribution function. In the rotationally symmetric state, we show that the Bardasis-Schrieffer mode, corresponding to the subdominant pairing, hybridizes with the nematic collective mode and merges into a single in-gap mode, with the mixing vanishing only close to the phase boundaries. For the d-wave ground state, we find that nematic interaction suppresses the damping of the collective oscillations in the short-time dynamics. Additionally, we find that even inside the nematic s+d-wave superconducting state, a Bardasis-Schrieffer-like mode leads to order parameter oscillations that strongly depend on the competition between the two pairing symmetries. We discuss the connection of our results to the recent pump-probe experiments on high-Tc superconductors.
[1] Marvin A. Mueller, Pengtao Shen, Maxim Dzero, Ilya M. Eremin, Phys. Rev. B 98 024522 (2018)
[2] Marvin A. Müller, Pavel A. Volkov, Indranil Paul, Ilya M. Eremin,Phys. Rev. B 100 , 140501(R) (2019)
[2] Marvin A. Müller, Pavel A. Volkov, Indranil Paul, Ilya M. Eremin, arXiv:2011.01042