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 Na$_2$IrO$_3$. We show that, on the picosecond timescale, the photoinjected electron-hole pairs delocalize on the hexagons of the Ir lattice via the formation of quasi-molecular orbital (QMO) excitations and the exchange of energy with the short-range-ordered zig-zag 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 new 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. 
Nicola Nembrini, Simone Peli, Francesco Banfi, Gabriele Ferrini,   Yogesh Singh, Philipp Gegenwart, Riccardo Comin, Kateryna...
cond-mat.str-el