Momentum-selective phononic response at ultrafast antiferromagnetic dynamics

This proposal investigates phonon dynamics following photoexcitation that demagnetizes antiferromagnetic (AFM) CuO. Using time-resolved magnetic diffuse scattering, we recently clarified that the demagnetization leads to magnon creation in a large reciprocal-space volume and that the magnons spontaneously condense at the Γ point with a spin gap. Further relaxation processes to annihilate magnons are likely mediated by phonon emission, which should be exclusive in momentum (q) because of the energy conservation rule. Therefore, we expect q-selective phonon excitation on the timescale of magnon annihilation. To verify this, we propose performing time-resolved diffuse scattering, witch has both time- and q-resolution. The achievement will allow us (1) to establish the reciprocal-space picture of the recovery process from a photo-created non-equilibrium AFM state, which will form the basis of AFM-based spintronics, and (2) to extract the mode-selective magnon-phonon coupling strength.