Title: Hund's coupling driven photo-carrier relaxation in the two-band Mott insulator,
Abstract: We study the relaxation dynamics of photo-carriers in the paramagnetic Mott
insulating phase of the half-filled two-band Hubbard model. Using
nonequilibrium dynamical mean field theory, we excite charge carriers across
the Mott gap by a short hopping modulation, and simulate the evolution of the
photo-doped population within the Hubbard bands. We observe an ultrafast
charge-carrier relaxation driven by emission of local spin excitations with an
inverse relaxation time proportional to the Hund's coupling. The photo-doping
generates additional side-bands in the spectral function, and for strong Hund's
coupling, the photo-doped population also splits into several resonances. The
dynamics of the local many-body states reveals two effects, thermal blocking
and kinetic freezing, which manifest themselves when the Hund's coupling
becomes of the order of the temperature or the bandwidth, respectively. These
effects, which are absent in the single-band Hubbard model, should be relevant
for the interpretation of experiments on correlated materials with multiple
active orbitals. In particular, the features revealed in the non-equilibrium
energy distribution of the photo-carriers are experimentally accessible, and
provide information on the role of the Hund's coupling in these materials.