Nonequilibrium melting of spin and orbital-order in the two-band Hubbard model

We study the dynamics of spin and orbital order after strong non-equilibrium excitation in a two-band Hubbard model, using non-equilibrium dynamical mean field theory. The model features an A-type antiferromagnetic phase with antiferro-orbital ordering in equilibrium. Various charge excitations are created during the strong electric pulse, causing both spin and orbital order to melt dynamically. However, due to strong anisotropy in the hopping of electrons in the ordered phase, the orbital-order defects are easier to create and move than the spin-order defects. Therefore, the antiferromagnetic order typically melts slower than the antiferro-orbital order. In addition, varying Hund's coupling modifies the energy spectrum of the two-electron sector in the local Hilbert space. We demonstrate that this can be utilized to control the relative populations of non-equilibrium excitations and therefore the dynamical melting of order parameters. Our finding reveals the possibility of preparing non-thermal spin and orbital-ordered phases and may lead to a way of simultaneously controlling the order parameters with non-equilibrium techniques.