Ultrafast many-body correlations in an excitonic insulator out of equilibrium

A fast time propagation method for nonequilibrium Green's functions [1] based on the generalized Kadanoff-Baym Ansatz (GKBA) [2] is applied to a lattice system with a symmetry-broken equilibrium phase, namely an excitonic insulator [3]. The adiabatic preparation of a correlated symmetry-broken initial state from a Hartree-Fock wave function within GKBA is assessed by comparing with a solution of the imaginary-time Dyson equation [4]. We find that it is possible to reach a symmetry-broken correlated initial state with nonzero excitonic order parameter by the adiabatic switching procedure. We discuss under which circumstances this is possible in practice within reasonably short switching times. We further investigate the out-of-equilibrium dynamics of competing orders and how the balance between them could be controlled by laser driving [5].

[1] G. Stefanucci and R. van Leeuwen, Nonequilibrium many-body theory of quantum systems, CUP (2013)
[2] P. Lipavský et al., Phys. Rev. B 34, 6933 (1986)
[3] D. Golez et al., Phys. Rev. B 94, 035121 (2016)
[4] R. Tuovinen et al., arXiv:1808.00712 (accepted Phys. Status Solidi)
[5] R. Tuovinen et al., in preparation.