Flat bands from hetero‑biaxial strain moiré in bilayer graphene without relaxation

Determine whether bilayer graphene moiré superlattices generated solely by hetero‑biaxial strain applied to one layer, without atomic relaxation, can host low‑energy flat bands comparable to those observed at magic angles in twisted bilayer graphene, or establish conditions under which such flat bands cannot form.

Background

The authors show that moiré patterns in twisted bilayer graphene (TBG) produce flat bands at magic angles due to strong localization in AA regions, leading to pronounced small‑velocity transport regimes and correlated phenomena. They contrast this with moiré superlattices formed by hetero‑biaxial strain in one layer, reporting unsuccessful attempts to obtain similar flat bands when atomic relaxation is turned off.

This raises a targeted question about the fundamental capability of strain‑induced moiré patterns (without relaxation) to create flat bands, as compared to rotation‑induced moiré, and motivates a precise determination or no‑go result for such band flattening mechanisms.

References

For example, we have not been able to obtain similar flat bands by calculations using the TB model for bilayer graphene with the similar moir e size but resulting from biaxial strain of one of the two layers (hetero-biaxial strain) without atomic relaxation.

— Electronic structure and transport in materials with flat bands: 2D materials and quasicrystals (2506.06721 - Laissardière et al., 7 Jun 2025) in Subsection "Low-energy flat bands in magic angle twisted bilayer graphene" (Sec_flatBands_in_tBLG)