Microscopic theory for electron-phonon coupling in twisted bilayer graphene
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arXiv
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| Formato: | Preprint |
| Publicado: |
2024
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| _version_ | 1866912897320353792 |
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| author | Zhu, Ziyan Devereaux, Thomas P. |
| author_facet | Zhu, Ziyan Devereaux, Thomas P. |
| contents | The origin of superconductivity in twisted bilayer graphene -- whether phonon-driven or electron-driven -- remains unresolved, in part due to the absence of a quantitative and efficient model for electron-phonon coupling (EPC). In this work, we develop a first-principles-based microscopic theory to calculate EPC in twisted bilayer graphene for arbitrary twist angles without requiring a periodic moiré supercell. Our approach combines a momentum-space continuum model for both electronic and phononic structures with a generalized Eliashberg-McMillan theory beyond the adiabatic approximation. Using this framework, we find that the EPC is strongly enhanced near the magic angle. The superconducting transition temperature induced by low-energy phonons peaks at $1.1^\circ$ around 1 K, and remains finite for a range of angles both below and above the magic angles. We predict that superconductivity persists up to $\sim 1.4^\circ$, where superconductivity has been recently observed despite the dispersive electronic bands. Beyond a large density of states, we identify a key condition for strong EPC: resonance between the electronic bandwidth and the dominant phonon frequencies. We also show that the EPC strength of a specific phonon corresponds to the modification of the moiré potential. In particular, we identify several $Γ$-phonon branches that contribute most significantly to the EPC, which are experimentally detectable via Raman spectroscopy. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2407_03293 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Microscopic theory for electron-phonon coupling in twisted bilayer graphene Zhu, Ziyan Devereaux, Thomas P. Mesoscale and Nanoscale Physics Strongly Correlated Electrons Superconductivity The origin of superconductivity in twisted bilayer graphene -- whether phonon-driven or electron-driven -- remains unresolved, in part due to the absence of a quantitative and efficient model for electron-phonon coupling (EPC). In this work, we develop a first-principles-based microscopic theory to calculate EPC in twisted bilayer graphene for arbitrary twist angles without requiring a periodic moiré supercell. Our approach combines a momentum-space continuum model for both electronic and phononic structures with a generalized Eliashberg-McMillan theory beyond the adiabatic approximation. Using this framework, we find that the EPC is strongly enhanced near the magic angle. The superconducting transition temperature induced by low-energy phonons peaks at $1.1^\circ$ around 1 K, and remains finite for a range of angles both below and above the magic angles. We predict that superconductivity persists up to $\sim 1.4^\circ$, where superconductivity has been recently observed despite the dispersive electronic bands. Beyond a large density of states, we identify a key condition for strong EPC: resonance between the electronic bandwidth and the dominant phonon frequencies. We also show that the EPC strength of a specific phonon corresponds to the modification of the moiré potential. In particular, we identify several $Γ$-phonon branches that contribute most significantly to the EPC, which are experimentally detectable via Raman spectroscopy. |
| title | Microscopic theory for electron-phonon coupling in twisted bilayer graphene |
| topic | Mesoscale and Nanoscale Physics Strongly Correlated Electrons Superconductivity |
| url | https://arxiv.org/abs/2407.03293 |