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.
Highlights
Effects of electron-phonon interactions (EPI) in metals and superconductors are most accurately modeled by the Eliashberg formalism [1,2]
We focus on systems with one or more flat electron energy bands close to the Fermi level, where the term “flatness” is to be understood in comparison to the phonon energy scale
Calculating angular resolved photoemission spectroscopy (ARPES) and STS/STM spectra using full-bandwidth Eliashberg theory, we reveal a sequence of quasiparticle replica bands outside the electron bandwidth W of the flat bands, occurring both at positive and negative frequencies
Summary
Effects of electron-phonon interactions (EPI) in metals and superconductors are most accurately modeled by the Eliashberg formalism [1,2] The connection between this theory and scanning tunneling spectroscopy/microscopy (STS/STM) spectra has been well understood for many decades [3,4]. Advances in angular resolved photoemission spectroscopy (ARPES) have led to the possibility of an even richer comparison between theory and experiment [5,6,7,8] These techniques have been successfully applied to gain better understanding of many materials, such as the high-temperature superconducting cuprates [9,10,11,12] and monolayer FeSe on a SrTiO3 (STO) substrate [13,14,15], to name only few examples.
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