Anomalous suppression of photoinduced in-gap weight in the optical conductivity of a two-leg Hubbard ladder

Photoinduced nonequilibrium states in the Mott insulators reflect the fundamental nature of competition between itinerancy and localization of the charge degrees of freedom. The spin degrees of freedom will also contribute to the competition in a different manner depending on lattice geometry. We investigate pulse-excited optical responses of a half-filled two-leg Hubbard ladder [1]. Calculating the time-dependent optical conductivity by time-dependent density matrix renormalization group, we find that strong monocycle pulse inducing quantum tunneling gives rise to anomalous suppression of photo-induced in-gap weight, leading to negative weight. This is in contrast to finite positive weight in the Hubbard chain. The origin of this anomalous behavior in the two-leg ladder is attributed to photoinduced localized exciton in the time-dependent wavefunctions, which reflects strong spin-singlet dimer correlation in the ground state.

[1] T. Tohyama, K. Shinjo, S. Sota, and S. Yunoki, Phys. Rev. B 108, 035113 (2023).