Distinct mechanisms for coherent magnon generation in a correlated van der Waals antiferromagnet

In recent decades, ultrashort optical pulses have emerged as an important tool for manipulating magnetic dynamics in antiferromagnets. Strongly correlated materials in particular offer intriguing possibilities for unconventional pathways to launch collective spin excitations due to their highly intertwined degrees of freedom. In this talk, I will discuss distinct mechanisms for the generation of a coherent magnon in the correlated van der Waals antiferromagnet NiPS₃. This compound features a rich spectrum of below-gap electronic transitions, including spin–orbit-entangled excitons that are strongly coupled to the long-range antiferromagnetic order. We demonstrate using ultrafast terahertz spectroscopy that the non-equilibrium driving of these dressed excitons leads to a coherent spin precession. Moreover, we observe that this same magnon mode can be excited via markedly different mechanisms as we tune the pump photon energy across a broad range of the optical spectrum. Our results suggest a strategy for controlling magnon dynamics based on the selective photoexcitation of electronic states.