Kekulé spiral order at all nonzero integer fillings in twisted bilayer graphene

Journal article

We study magic angle graphene in the presence of both strain and particle-hole symmetry breaking due to non-local inter-layer tunneling. We perform a self-consistent Hartree-Fock study that incorporates these effects alongside realistic interaction and substrate potentials, and explore a comprehensive set of competing orders including those that break translational symmetry at arbitrary wavevectors. We find that at all non-zero integer fillings very small strains, comparable to those measured in scanning tunneling experiments, stabilize a fundamentally new type of time-reversal symmetric and spatially non-uniform order. This order, which we dub the 'incommensurate Kekulé spiral' (IKS) order, spontaneously breaks both the emergent valley-charge conservation and moiré translation symmetries, but preserves a modified translation symmetry T^′ -- which simultaneously shifts the spatial coordinates and rotates the U(1) angle which characterizes the spontaneous inter-valley coherence. We discuss the phenomenological and microscopic properties of this order. We argue that our findings are consistent with all experimental observations reported so far, suggesting a unified explanation of the global phase diagram in terms of the IKS order.

Authors: Kwan, YH; Wagner, G; Soejima, T; Zaletel, MP; Simon, SH

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Physical Society
• Journal: Physical Review X
• Volume: 11
• Issue: 4
• Article number: 041063
• Publication date: 2021-12-30
• Acceptance date: 2021-11-08
• DOI: 10.1103/PhysRevX.11.041063
• ISSN: 2160-3308
• Language: English
• Keywords: cond-mat.mes-hall; cond-mat.str-el; FFR