Tracking local magnetic dynamics via high-energy charge excitations in a relativistic Mott insulator

We use time- and energy-resolved optical spectroscopy to investigate the coupling of electron-hole excitations to the magnetic environment in the relativistic Mott insulator Na2IrO3. We show that, on the picosecond time scale, the photoinjected electron-hole pairs delocalize on the hexagons of the Ir lattice via the formation of quasimolecular orbital excitations and the exchange of energy with the short-range-ordered zigzag magnetic background. The possibility of mapping the magnetic dynamics, which is characterized by typical frequencies in the THz range, onto high-energy (1-2 eV) charge excitations provides a platform to investigate, and possibly control, the dynamics of magnetic interactions in correlated materials with strong spin-orbit coupling, even in the presence of complex magnetic phases.