Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium



: Tuovinen R, Golez D, Eckstein M, Sentef MA

Publisher: AMER PHYSICAL SOC

: 2020

: Physical Review B

: PHYSICAL REVIEW B

: PHYS REV B

: ARTN 115157

: 102

: 11

: 13

: 2469-9950

: 2469-9969

DOI: https://doi.org/10.1103/PhysRevB.102.115157

: https://research.utu.fi/converis/portal/detail/Publication/50451631


We investigate out-of-equilibrium dynamics in an excitonic insulator (EI) with a finite-momentum pairing perturbed by a laser-pulse excitation and a sudden coupling to fermionic baths. The transient dynamics of the excitonic order parameter is resolved using the full nonequilibrium Green's function approach and the generalized Kadanoff-Baym ansatz (GKBA) within the second-order Born approximation. The comparison between the two approaches after a laser-pulse excitation shows a good agreement in the weak and the intermediate photodoping regime. In contrast, the laser-pulse dynamics resolved by the GKBA does not show a complete melting of the excitonic order after a strong excitation. Instead we observe persistent oscillations of the excitonic order parameter with a predominant frequency given by the renormalized equilibrium band gap. This anomalous behavior can be overcome within the GKBA formalism by coupling to an external bath, which leads to a transition of the EI system toward the normal state. We analyze the long-time evolution of the system and distinguish decay timescales related to dephasing and thermalization.

Last updated on 2024-26-11 at 23:22