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 Kekul\'e spiral' (IKS) order, spontaneously breaks both the emergent valley-charge conservation and moir\'e 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.
@article{arxiv.2105.05857,
title = {Kekul\'e spiral order at all nonzero integer fillings in twisted bilayer graphene},
author = {Yves H. Kwan and Glenn Wagner and Tomohiro Soejima and Michael P. Zaletel and Steven H. Simon and Siddharth A. Parameswaran and Nick Bultinck},
journal= {arXiv preprint arXiv:2105.05857},
year = {2022}
}
Comments
18pp + 6pp references, 8 figures (main text); 16pp, 22 figures (supplement); v3: published version