Dichotomy of Electron-Phonon Coupling in Graphene Moiré Flat Bands
- 11 October 2021
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 127 (16), 167001
- https://doi.org/10.1103/physrevlett.127.167001
Abstract
Graphene moiré superlattices are outstanding platforms to study correlated electron physics and superconductivity with exceptional tunability. However, robust superconductivity has been measured only in magic-angle twisted bilayer graphene (MA-TBG) and magic-angle twisted trilayer graphene (MA-TTG). The absence of a superconducting phase in certain moiré flat bands raises a question on the superconducting mechanism. In this work, we investigate electronic structure and electron-phonon coupling in graphene moiré superlattices based on atomistic calculations. We show that electron-phonon coupling strength is dramatically different among graphene moiré flat bands. The total strength is very large () for MA-TBG and MA-TTG, both of which display robust superconductivity in experiments. However, 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 that the Bernal-stacked layers in TDBG and TMBG induce sublattice polarization in the flat-band states, suppressing intersublattice electron-phonon matrix elements. We also obtain the nonadiabatic superconducting transition temperature that matches well with the experimental results. Our results clearly show a correlation between strong electron-phonon coupling and experimental observations of robust superconductivity.
Funding Information
- National Research Foundation of Korea (2020R1A2C3013673, 2017R1A5A1014862, 2017H1A2A1042152)
- Korea Institute of Science and Technology Information (KSC-2020-CRE-0335)
This publication has 52 references indexed in Scilit:
- Energy spectrum and quantum Hall effect in twisted bilayer graphenePhysical Review B, 2012
- Moiré bands in twisted double-layer grapheneProceedings of the National Academy of Sciences of the United States of America, 2011
- Flat bands in slightly twisted bilayer graphene: Tight-binding calculationsPhysical Review B, 2010
- Electronic structure of turbostratic graphenePhysical Review B, 2010
- Graphene Bilayer with a Twist: Electronic StructurePhysical Review Letters, 2007
- Registry-dependent interlayer potential for graphitic systemsPhysical Review B, 2005
- The phonon dispersion of graphite revisitedSolid State Communications, 2004
- Conductance of Crossed Carbon NanotubesJournal of the Physics Society Japan, 2001
- Improved tetrahedron method for Brillouin-zone integrationsPhysical Review B, 1994
- Symmetry Properties of the Normal Vibrations of a CrystalReviews of Modern Physics, 1968