Antiphase Oscillation in Time-Resolved Spin Structure Factor of a Photoexcited Mott Insulator

Motivated by recent development of time-resolved resonant-inelastic x-ray scattering (trRIXS) in photoexcited antiferromagnetic Mott insulators, we numerically investigate momentum-dependent transient spin dynamics in a half-filled Hubbard model on square lattice. After turning off pumping photon pulse, the intensity of dynamical spin structure factor temporally oscillates with frequencies determined by the energy of two magnons in the antiferromagnetic Mott insulator. We find an antiphase behavior in the oscillation between two orthogonal momentum directions, parallel and perpendicular to the electric field of pump pulse. The phase difference comes from the $B_{1\mathrm{g}}$ channel of the two-magnon excitation. Observing this antiphase oscillation will be a big challenge for tr-RIXS experiments when their time resolution will be improved by more than an order of magnitude.