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

TL;DR

This paper predicts a cascade of replica bands in flat band systems like twisted bilayer graphene due to electron-phonon interactions, providing a way to experimentally probe phonon energy scales and EPI effects.

Contribution

It introduces a theoretical framework for identifying replica bands in flat band systems and applies it specifically to twisted bilayer graphene, linking EPI to observable spectral features.

Findings

Replica bands originate from frequency-dependent electron mass renormalization.

Predicted replica bands can be used to determine phonon energy scales experimentally.

Application to twisted bilayer graphene suggests observable signatures of electron-phonon interactions.

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 Photo Emission Spectroscopy and Scanning Tunneling Spectroscopy/Microscopy 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.