Ultrafast Quenching of the Exchange Interaction in a Mott Insulator
  We investigate how fast and how effective photocarrier excitation can modify the exchange interaction $J_\mathrm{ex}$ in the prototype Mott-Hubbard insulator. We demonstrate an ultrafast quenching of $J_\mathrm{ex}$ both by evaluating exchange integrals from a time-dependent response formalism and by explicitly simulating laser-induced spin precession in an antiferromagnet that is canted by an external magnetic field. In both cases, the electron dynamics is obtained from nonequilibrium dynamical mean-field theory. We find that the modified $J_\mathrm{ex}$ emerges already within a few electron hopping times after the pulse, with a reduction that is comparable to the effect of chemical doping. 
J.H. Mentink and M. Eckstein
cond-mat.str-el