Nonequilibrium Dynamical Mean Field Theory for Inhomogeneous and Photo-Excited Systems*

Photodoping of a Mott insulator triggers a nonequilibrium phase transition from a correlation induced insulating state to a nonthermal conducting state with electron- and hole-like carriers. Using the nonequilibrium extension of (inhomogeneous) dynamical mean field theory\footnote{J. K. Freericks, V. M. Turkowski, and V. Zlatic, ``Nonequilibrium Dynamical Mean-Field Theory,'' Phys. Rev. Lett. 97, 266408 (2006).}$^,$\footnote{M. Eckstein and P. Werner, ``Nonequilibrium dynamical mean field simulation of inhomogeneous systems,'' Phys. Rev. B 88, 075135 (2013).} in combination with a strong-coupling impurity solver\footnote{M. Eckstein and P. Werner, ``Nonequilibrium dynamical mean-field calculations based on the non-crossing approximation and its generalizations,'' Phys. Rev. B 82, 115115 (2010).} we study the relaxation and diffusion of photo-doped carriers in Mott insulating bulk systems and hetero-structures. In large-gap insulators, the life-time of the carriers depends exponentially on the gap size,\footnote{M. Eckstein and P. Werner, ``Thermalization of a pump-excited Mott insulator,'' Phys. Rev. B 84, 035122 (2011).} while in small-gap insulators, strongly pulse-energy dependent impact ionization processes lead to a double-exponential relaxation.\footnote{P. Werner, K. Held and M. Eckstein, ``Role of impact ionization in the thermalization of photo-excited Mott insulators,'' arXiv:1408.3425.} In the paramagnetic phase, the photo-doped carriers spread through the insulator in a diffusive manner, while the scattering with an antiferromagnetic background leads to a rapid loss of kinetic energy.\footnote{P. Werner, N. Tsuji, and M. Eckstein, ``Nonthermal symmetry broken states in the strongly interacting Hubbard model,'' Phys. Rev. B 86, 205101 (2012).} In the presence of strong fields, as realized e. g. in polar heterostructures, the ability to dissipate energy locally in an antiferromagnetic system enables fast carrier transport.\footnote{M. Eckstein and P. Werner, ``Ultrafast separation of photo-doped carriers in Mott antiferromagnets,'' Phys. Rev. Lett. 113, 076405 (2014).} These insights should be relevant for designing Mott insulating solar cells\footnote{E. Assmann, P. Blaha, R. Laskowski, K. Held, S. Okamoto, and G. Sangiovanni, ``Oxide Heterostructures for Efficient Solar Cells,'' Phys. Rev. Lett. 110, 078701 (2013).} and light-controlled devices which operate on an ultra-fast timescale.