Antiphase oscillations in the time-resolved spin structure factor of a photoexcited Mott Insulator on a square lattice

We investigate momentum-dependent transient spin dynamics after photoirradiation in a two-dimensional Mott insulator described by a half-filled Hubbard model on a square lattice by using a numerically exact-diagonalization technique. We find a temporal oscillation in the static spin structure factor of a square-root 18 times square-root 18 periodic lattice. The oscillation exhibits an antiphase behavior between, for example, two orthogonal momentum directions parallel and perpendicular to the electric field of a pump pulse. The origin of the antiphase oscillation is attributed to a photoexcited wave function that has overlap with eigenstates producing the B1g bimagnon Raman intensity. Observing such antiphase oscillations will be a big challenge for time-resolved resonant elastic x-ray scattering experiments.