Interacting Electrons in a Flat‐Band System within the Generalized Kadanoff–Baym Ansatz

In this work, the study of the spectral properties of an open interacting system by solving the generalized Kadanoff-Baym ansatz (GKBA) master equation for the single-particle density matrix, namely the time-diagonal lesser Green's function, is reported. To benchmark its validity, the solution obtained within the GKBA is compared with the solution of the Dyson equation at stationarity. In both approaches, the interaction is treated within the self-consistent second-order Born approximation, whereas the GKBA still retains the retarded propagator calculated at the Hartree-Fock (HF) and wideband limit approximation level. The model chosen is that of two leads connected through a central correlated region where particles can interact and utilize the stationary particle current at the boundary of the junction as a probe of the spectral features of the system. The central region is chosen as the simplest model featuring a degenerate ground state with a flat band. The main result is that the solution of the GKBA master equation captures well the spectral feature of such system and specifically the transition from dispersionless to dispersive behavior of the flat band as the interaction is increased. Therefore, the GBKA solution retains the main spectral features of the self-energy used even when the propagator is at the HF level.Herein, the nonequilibrium Green's function approach is employed to study transport across a correlated 1D system featuring a flat band in its single-particle energy spectrum. Specifically, the results of the solution of the stationary Dyson equation are compared with those obtained by the generalized Kadanoff-Baym ansatz (GKBA) master equation. Good agreement is found between the two although the GBKA approach used here does not account for correlations in the retarded propagator. Strikingly, the restoration of transport is observed through the otherwise nonconductive flat band.image (c) 2024 WILEY-VCH GmbH