The Flexoelectric Twist: Persistence of Heavy Fermion Picture in Small-Angle Twisted Bilayer Graphene
Abstract
Twisted bilayer graphene (TBG) near the first magic angle (θ≈1.05∘) hosts flat bands that provide a fertile ground for exploring strongly correlated and topological phases. At smaller twist angles (θ<1∘), attice relaxation profoundly alters the moiré landscape. The extent to which moiré lattice reconstruction at different length scales affects the electronic structure through electro-mechanical coupling remains unresolved. Here, using scanning tunneling microscopy on small-angle TBG devices (θ≈0.3−0.7∘), we observe a pronounced dI/dV peak at the AA site of the moiré lattice on top of a spectrum that is asymmetric about the charge neutrality point, lattice reconstruction over moiré lattice length scales, as well as a dilation of the atomic lattice at the AA sites. We demonstrate at a phenomenological level that the inclusion of moiré lattice reconstruction supports compact localized heavy fermion f− states localized at AA sites. The additional inclusion of atomic lattice dilation enerates a strong flexo-electric response that explicitly breaks particle-hole symmetry, pushing compact, localized f-states at the AA sites down in energy. Consequently, these heavy fermion states energetically coexist with itinerant c-electrons at the AB/BA sites. Our spatially resolved spectroscopic measurements quantitatively visualize this coexistence, confirming the persistence of the heavy fermion model in the small-angle regime θ<1∘. Our findings provide microscopic insights into how flexo-electricity affects the low-energy electronic structure of small-angle TBG. More broadly, our study establishes small-angle TBG as a new class of moiré materials to explore the interacting Kondo lattice problem with high tunability of the f−occupation and c−density through twist-angle and electrostatic back gates, respectively.
Related
- Monopole-Fermion Scattering from Twisted Conformal Boundary States
- Randomly twisted bilayer graphene: Cascade transitions
- Phase-sensitive signatures of time-reversal-symmetry-breaking superconductivity in magic-angle twisted trilayer graphene
- Dirac Fermion Scattering and Conductance Response in Asymmetric Graphene Wormholes
- Composite Fermion Theory of Fractional Chern Insulators in Rhombohedral Graphene
BibTeX
@misc{yao2026flexoelectric,
title = {{The Flexoelectric Twist: Persistence of Heavy Fermion Picture in Small-Angle Twisted Bilayer Graphene}},
author = {Qirong Yao and Ka Cheuk Fan and Tianyu Qiao and Hao Shi and Xi Dai and Berthold Jäck},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.38305},
eprint = {2610.38305},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.38305},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - The Flexoelectric Twist: Persistence of Heavy Fermion Picture in Small-Angle Twisted Bilayer Graphene
AU - Qirong Yao
AU - Ka Cheuk Fan
AU - Tianyu Qiao
AU - Hao Shi
AU - Xi Dai
AU - Berthold Jäck
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2610.38305
UR - https://arxiv.org/abs/2610.38305
AB - Twisted bilayer graphene (TBG) near the first magic angle (θ≈1.05^∘) hosts flat bands that provide a fertile ground for exploring strongly correlated and topological phases. At smaller twist angles (θ<1^∘), attice relaxation profoundly alters the moiré landscape. The extent to which moiré lattice reconstruction at different length scales affects the electronic structure through electro-mechanical coupling remains unresolved. Here, using scanning tunneling microscopy on small-angle TBG devices (θ≈0.3−0.7^∘), we observe a pronounced dI/dV peak at the AA site of the moiré lattice on top of a spectrum that is asymmetric about the charge neutrality point, lattice reconstruction over moiré lattice length scales, as well as a dilation of the atomic lattice at the AA sites. We demonstrate at a phenomenological level that the inclusion of moiré lattice reconstruction supports compact localized heavy fermion f− states localized at AA sites. The additional inclusion of atomic lattice dilation enerates a strong flexo-electric response that explicitly breaks particle-hole symmetry, pushing compact, localized f-states at the AA sites down in energy. Consequently, these heavy fermion states energetically coexist with itinerant c-electrons at the AB/BA sites. Our spatially resolved spectroscopic measurements quantitatively visualize this coexistence, confirming the persistence of the heavy fermion model in the small-angle regime θ<1^∘. Our findings provide microscopic insights into how flexo-electricity affects the low-energy electronic structure of small-angle TBG. More broadly, our study establishes small-angle TBG as a new class of moiré materials to explore the interacting Kondo lattice problem with high tunability of the f−occupation and c−density through twist-angle and electrostatic back gates, respectively.
ER -