A1 Refereed original research article in a scientific journal
Comparing the generalized Kadanoff-Baym ansatz with the full Kadanoff-Baym equations for an excitonic insulator out of equilibrium
Authors: Tuovinen R, Golez D, Eckstein M, Sentef MA
Publisher: AMER PHYSICAL SOC
Publication year: 2020
Journal: Physical Review B
Journal name in source: PHYSICAL REVIEW B
Journal acronym: PHYS REV B
Article number: ARTN 115157
Volume: 102
Issue: 11
Number of pages: 13
ISSN: 2469-9950
eISSN: 2469-9969
DOI: https://doi.org/10.1103/PhysRevB.102.115157
Self-archived copy’s web address: 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.
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