Abstract
We investigate phonon-mediated Cooper pairing in flat electronic band systems by solving the full-bandwidth multiband Eliashberg equations for superconductivity in magic angle twisted bilayer graphene using a realistic tight-binding model. We find that Cooper pairing away from the Fermi level contributes decisively to superconductivity by enhancing the critical temperature and ensures a robust finite superfluid density. We show that this pairing yields particle-hole asymmetric superconducting domes in the temperature-gating phase diagram and gives rise to distinct spectroscopic signatures in the superconducting state. We predict several such features in tunneling and angle resolved photoemission spectra for future experiments.
Highlights
We investigate phonon-mediated Cooper pairing in flat electronic band systems by solving the full-bandwidth multiband Eliashberg equations for superconductivity in magic angle twisted bilayer graphene using a realistic tight-binding model
We focus on magic angle twisted bilayer graphene (TBG), a prototypical flat band superconductor, that has recently attracted tremendous research interest due to the rich variety of physical phenomena that result from a vastly changed electronic structure depending on the twist angle [9,10,11,12,13,14,15]
There is a competition with external gating between the superconducting and an insulating state [10,11]. The latter is associated with enhanced correlations that manifest as extended features seen by tunneling experiments in the nonsuperconducting state of TBG [17,18,19]
Summary
We investigate phonon-mediated Cooper pairing in flat electronic band systems by solving the full-bandwidth multiband Eliashberg equations for superconductivity in magic angle twisted bilayer graphene using a realistic tight-binding model. Full-bandwidth Eliashberg calculations of superconductivity in TBG having as input realistic electron dispersions and EPI. In contrast to the BCS picture, (ω) > 0 throughout the full bandwidth and show that Cooper pairing stems primarily from electrons away from the Fermi level.
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