Helical trilayer graphene: a moiré platform for strongly-interacting topological bands
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| Main Authors: | , , , , , , , , , , , |
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| Format: | Preprint |
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2023
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| _version_ | 1866908510713806848 |
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| author | Xia, Li-Qiao de la Barrera, Sergio C. Uri, Aviram Sharpe, Aaron Kwan, Yves H. Zhu, Ziyan Watanabe, Kenji Taniguchi, Takashi Goldhaber-Gordon, David Fu, Liang Devakul, Trithep Jarillo-Herrero, Pablo |
| author_facet | Xia, Li-Qiao de la Barrera, Sergio C. Uri, Aviram Sharpe, Aaron Kwan, Yves H. Zhu, Ziyan Watanabe, Kenji Taniguchi, Takashi Goldhaber-Gordon, David Fu, Liang Devakul, Trithep Jarillo-Herrero, Pablo |
| contents | Quantum geometry of electronic wavefunctions results in fascinating topological phenomena. A prominent example is the intrinsic anomalous Hall effect (AHE) in which a Hall voltage arises in the absence of an applied magnetic field. The AHE requires a coexistence of Berry curvature and spontaneous time-reversal symmetry breaking. These conditions can be realized in two-dimensional moiré systems with broken $xy$-inversion symmetry ($C_{2z}$) that host flat electronic bands. Here, we explore helical trilayer graphene (HTG), three graphene layers twisted sequentially by the same angle forming two misoriented moiré patterns. Although HTG is globally $C_{2z}$-symmetric, surprisingly we observe clear signatures of topological bands. At a magic angle $θ_\mathrm{m}\approx 1.8^\circ$, we uncover a robust phase diagram of correlated and magnetic states using magnetotransport measurements. Lattice relaxation leads to large periodic domains in which $C_{2z}$ is broken on the moiré scale. Each domain harbors flat topological bands with valley-contrasting Chern numbers $\pm(1,-2)$. We find correlated states at integer electron fillings per moiré unit cell $ν=1,2,3$ and fractional fillings $2/3,7/2$ with the AHE arising at $ν=1,3$ and $2/3,7/2$. At $ν=1$, a time-reversal symmetric phase appears beyond a critical electric displacement field, indicating a topological phase transition. Finally, hysteresis upon sweeping $ν$ points to first-order phase transitions across a spatial mosaic of Chern domains separated by a network of topological gapless edge states. We establish HTG as an important platform that realizes ideal conditions for exploring strongly interacting topological phases and, due to its emergent moiré-scale symmetries, demonstrates a novel way to engineer topology. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2310_12204 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Helical trilayer graphene: a moiré platform for strongly-interacting topological bands Xia, Li-Qiao de la Barrera, Sergio C. Uri, Aviram Sharpe, Aaron Kwan, Yves H. Zhu, Ziyan Watanabe, Kenji Taniguchi, Takashi Goldhaber-Gordon, David Fu, Liang Devakul, Trithep Jarillo-Herrero, Pablo Mesoscale and Nanoscale Physics Strongly Correlated Electrons Quantum geometry of electronic wavefunctions results in fascinating topological phenomena. A prominent example is the intrinsic anomalous Hall effect (AHE) in which a Hall voltage arises in the absence of an applied magnetic field. The AHE requires a coexistence of Berry curvature and spontaneous time-reversal symmetry breaking. These conditions can be realized in two-dimensional moiré systems with broken $xy$-inversion symmetry ($C_{2z}$) that host flat electronic bands. Here, we explore helical trilayer graphene (HTG), three graphene layers twisted sequentially by the same angle forming two misoriented moiré patterns. Although HTG is globally $C_{2z}$-symmetric, surprisingly we observe clear signatures of topological bands. At a magic angle $θ_\mathrm{m}\approx 1.8^\circ$, we uncover a robust phase diagram of correlated and magnetic states using magnetotransport measurements. Lattice relaxation leads to large periodic domains in which $C_{2z}$ is broken on the moiré scale. Each domain harbors flat topological bands with valley-contrasting Chern numbers $\pm(1,-2)$. We find correlated states at integer electron fillings per moiré unit cell $ν=1,2,3$ and fractional fillings $2/3,7/2$ with the AHE arising at $ν=1,3$ and $2/3,7/2$. At $ν=1$, a time-reversal symmetric phase appears beyond a critical electric displacement field, indicating a topological phase transition. Finally, hysteresis upon sweeping $ν$ points to first-order phase transitions across a spatial mosaic of Chern domains separated by a network of topological gapless edge states. We establish HTG as an important platform that realizes ideal conditions for exploring strongly interacting topological phases and, due to its emergent moiré-scale symmetries, demonstrates a novel way to engineer topology. |
| title | Helical trilayer graphene: a moiré platform for strongly-interacting topological bands |
| topic | Mesoscale and Nanoscale Physics Strongly Correlated Electrons |
| url | https://arxiv.org/abs/2310.12204 |