Supermoiré Formation and Robust Topological Edge State in Helical Trilayer Graphene
Abstract
When two materials with nearly matched lattice constants meet, they form commensurate domains separated by incommensurate domain walls that absorb the mismatch. Recently, this picture has been extended to moiré lattices: when two moiré superlattices have nearly equal periodicities, they can form a "supermoiré" consisting of commensurate moiré domains separated by domain walls. Helical trilayer graphene (HTG) is a particularly interesting example: theory predicts that its commensurate domains are distinct topological insulators, separated by a network of conducting domain walls. Here, we use scanning tunneling microscopy and spectroscopy to visualize supermoiré domains and their electronic properties in HTG at a twist angle of ∼1.7∘. We find atomic-scale evidence of relaxation into supermoiré domains, each hosting flat bands separated from remote bands by large gaps of ∼40 meV. Domain walls exhibit spectrally uniform edge states along their length, in excellent agreement with calculations for valley-protected topological edge modes. The topological character of the flat bands is intimately tied to wavefunction localization on a graphene sublattice, and we reveal the topological change across a domain boundary by imaging the reversal of sublattice polarization.
Related
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BibTeX
@misc{li2026supermoiré,
title = {{Supermoiré Formation and Robust Topological Edge State in Helical Trilayer Graphene}},
author = {Hong Li and Huandong Chen and Seongyeon Youn and Kenji Watanabe and Takashi Taniguchi and Trithep Devakul and Kazuhiro Fujita and Abhay Narayan Pasupathy},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.07435},
eprint = {2611.07435},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.07435},
}
RIS
TY - UNPB
TI - Supermoiré Formation and Robust Topological Edge State in Helical Trilayer Graphene
AU - Hong Li
AU - Huandong Chen
AU - Seongyeon Youn
AU - Kenji Watanabe
AU - Takashi Taniguchi
AU - Trithep Devakul
AU - Kazuhiro Fujita
AU - Abhay Narayan Pasupathy
PY - 2026
DA - 2026/11/05
PB - arXiv
DO - 10.48550/arxiv.2611.07435
UR - https://arxiv.org/abs/2611.07435
AB - When two materials with nearly matched lattice constants meet, they form commensurate domains separated by incommensurate domain walls that absorb the mismatch. Recently, this picture has been extended to moiré lattices: when two moiré superlattices have nearly equal periodicities, they can form a "supermoiré" consisting of commensurate moiré domains separated by domain walls. Helical trilayer graphene (HTG) is a particularly interesting example: theory predicts that its commensurate domains are distinct topological insulators, separated by a network of conducting domain walls. Here, we use scanning tunneling microscopy and spectroscopy to visualize supermoiré domains and their electronic properties in HTG at a twist angle of ∼1.7^∘. We find atomic-scale evidence of relaxation into supermoiré domains, each hosting flat bands separated from remote bands by large gaps of ∼40 meV. Domain walls exhibit spectrally uniform edge states along their length, in excellent agreement with calculations for valley-protected topological edge modes. The topological character of the flat bands is intimately tied to wavefunction localization on a graphene sublattice, and we reveal the topological change across a domain boundary by imaging the reversal of sublattice polarization.
ER -