Abstract:
Recent advances in ultrafast studies have opened up new possibilities for controlling the microscopic interactions in quantum materials using light. One particularly exciting direction is Floquet engineering, in which periodic light fields dynamically tune the parameters of a material's Hamiltonian. In magnetic insulators, sub-gap laser pulses can modify spin-exchange interactions via virtual excitations, avoiding heating or real carrier generation.
In this talk, I will introduce a new mechanism called spin-mediated impulsive stimulated Raman scattering (spin-ISRS), where ultrafast light pulses induce a transient change in the magnetic exchange energy, which in turn drives coherent phonon oscillations. We experimentally demonstrate this effect in the antiferromagnetic insulator MnPS₃ using time-resolved broadband reflection spectroscopy, which shows a non-trivial temperature dependence beyond conventional mechanisms. Supported by a Floquet-based theoretical framework, our results suggest that sub-gap optical driving transiently enhances antiferromagnetic exchange interactions, leading to an additional spin-originated driving force on the lattice. This study highlights a new way to probe light-induced changes in the spin Hamiltonian, with implications for practical ways to control magnetic properties in quantum materials on ultrafast timescales.