Identify the microscopic origin of sub-picosecond rise-time dynamics in NiPS3

Ascertain the precise microscopic origin of the sub-picosecond rise-time dynamics (approximately 224–293 fs) observed in transient reflectivity measurements of NiPS3 under 3.1 eV optical pumping, determining the underlying processes responsible for the ultrafast signal onset beyond qualitative trends attributed to excitation-energy-dependent charge-transfer.

Background

The authors report sub-picosecond rise times that are significantly faster than previous broadband transient reflectivity studies at lower pump photon energies. Earlier work suggested a dependence on excitation-energy-driven charge-transfer between S 3p and Ni 3d orbitals, but a definitive microscopic mechanism for the observed ultrafast onset in NiPS3 remains unresolved.

Establishing the microscopic pathway responsible for such rapid dynamics is essential for accurately modeling exciton formation and early-time relaxation in correlated 2D antiferromagnets and for linking ultrafast optical responses to spin–charge–orbital interactions.