Electron-phonon coupling and superconductivity in twisted graphene layers

  We investigate electronic structures and electron-phonon interaction in twisted graphene layers based on atomistic calculations^[1-3]. We show electron-phonon coupling strength λ is dramatically different among twisted graphene layers. The total strength λ is very large for magic-angle twisted bilayer graphene and magic-angle twisted trilayer graphene, both of which display robust superconductivity in experiments. However, λ is an order of magnitude smaller in twisted double bilayer graphene (TDBG) and twisted monolayer-bilayer graphene (TMBG) where superconductivity is reportedly rather weak or absent. We find the Bernal-stacked layers in TDBG and TMBG induce sublattice polarization of electronic states, suppressing electron-phonon interaction. Our results suggest that the electron-phonon coupling may play an important role in the superconductivity of twisted graphene layers. This work was supported by NRF of Korea (Grants No. 2020R1A2C3013673 and No. 2017R1A5A1014862).

*Ref:
 ^[1] Y. W. Choi and H. J. Choi, Phys. Rev. B 98, 241412 (2018). [arXiv:1809.08407]
 ^[1] Y. W. Choi and H. J. Choi, Phys. Rev. B 100, 201402 (2019). [arXiv:1903.00852]
 ^[3] Y. W. Choi and H. J. Choi, Phys. Rev. Lett. 127, 167001 (2021). [arXiv:2103.16132]