Electron-phonon coupling and competing Kekulé orders in twisted bilayer graphene
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| Main Authors: | , , , , , |
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| Format: | Preprint |
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2023
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| _version_ | 1866915137334542336 |
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| author | Kwan, Yves H. Wagner, Glenn Bultinck, Nick Simon, Steven H. Berg, Erez Parameswaran, S. A. |
| author_facet | Kwan, Yves H. Wagner, Glenn Bultinck, Nick Simon, Steven H. Berg, Erez Parameswaran, S. A. |
| contents | Recent scanning tunneling microscopy experiments [K.P. Nuckolls et al., arXiv:2303.00024] have revealed the ubiquity of Kekulé charge-density wave order in magic-angle twisted bilayer graphene. Most samples are moderately strained and show `incommensurate Kekulé spiral' (IKS) order involving a graphene-scale charge density distortion uniaxially modulated on the scale of the moiré superlattice, in accord with theoretical predictions. However, ultra-low strain samples instead show graphene-scale Kekulé charge order that is uniform on the moiré scale. This order, especially prominent near filling factor $ν=-2$, is unanticipated by theory which predicts a time-reversal breaking Kekulé current order at low strain. We show that including the coupling of moiré electrons to graphene-scale optical zone-corner (ZC) phonons stabilizes a uniform Kekulé charge ordered state at $|ν|=2$ with a quantized topological (spin or anomalous Hall) response. Our work clarifies how this phonon-driven selection of electronic order emerges in the strong-coupling regime of moiré graphene. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2303_13602 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Electron-phonon coupling and competing Kekulé orders in twisted bilayer graphene Kwan, Yves H. Wagner, Glenn Bultinck, Nick Simon, Steven H. Berg, Erez Parameswaran, S. A. Strongly Correlated Electrons Mesoscale and Nanoscale Physics Recent scanning tunneling microscopy experiments [K.P. Nuckolls et al., arXiv:2303.00024] have revealed the ubiquity of Kekulé charge-density wave order in magic-angle twisted bilayer graphene. Most samples are moderately strained and show `incommensurate Kekulé spiral' (IKS) order involving a graphene-scale charge density distortion uniaxially modulated on the scale of the moiré superlattice, in accord with theoretical predictions. However, ultra-low strain samples instead show graphene-scale Kekulé charge order that is uniform on the moiré scale. This order, especially prominent near filling factor $ν=-2$, is unanticipated by theory which predicts a time-reversal breaking Kekulé current order at low strain. We show that including the coupling of moiré electrons to graphene-scale optical zone-corner (ZC) phonons stabilizes a uniform Kekulé charge ordered state at $|ν|=2$ with a quantized topological (spin or anomalous Hall) response. Our work clarifies how this phonon-driven selection of electronic order emerges in the strong-coupling regime of moiré graphene. |
| title | Electron-phonon coupling and competing Kekulé orders in twisted bilayer graphene |
| topic | Strongly Correlated Electrons Mesoscale and Nanoscale Physics |
| url | https://arxiv.org/abs/2303.13602 |