Prominent Cooper Pairing Away From the Fermi Level and its Spectroscopic Signature in Twisted Bilayer Graphene

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 [1]. We find that Cooper pairing away from the Fermi level [2] 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.

References:
[1] F. Schrodi, A. Aperis and P.M. Oppeneer, arXiv:1909.12532.
[2] A. Aperis and P.M. Oppeneer, Phys. Rev. B 97, 060501(R) (2018).