Cascade of replica bands in flat-band systems: Predictions for twisted bilayer graphene

Abstract

We investigate the effect of electron-phonon interactions (EPI) in systems exhibiting one or more flat electron bands close to the Fermi level and a comparatively large phonon energy scale. After solving the self-consistent full-bandwidth Eliashberg equations, we compute angular resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy/microscopy (STS/STM) spectra. We obtain a sequence of quasiparticle replica bands in both the normal and superconducting states that originate from frequency-dependent features of the electron mass renormalization function. We show that these replica bands can be used to extract the relevant phonon energy scale from experiments. Focusing in particular on twisted bilayer graphene, we predict replica-band formation, which, when observed, will shed light on the role of EPI in this archetypal flat-band system.