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




TekijätTuovinen R, Golez D, Eckstein M, Sentef MA

KustantajaAMER PHYSICAL SOC

Julkaisuvuosi2020

JournalPhysical Review B

Tietokannassa oleva lehden nimiPHYSICAL REVIEW B

Lehden akronyymiPHYS REV B

Artikkelin numeroARTN 115157

Vuosikerta102

Numero11

Sivujen määrä13

ISSN2469-9950

eISSN2469-9969

DOIhttps://doi.org/10.1103/PhysRevB.102.115157

Rinnakkaistallenteen osoitehttps://research.utu.fi/converis/portal/detail/Publication/50451631


Tiivistelmä
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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