Strain-induced Kekule spiral order in magic-angle graphene: a density matrix renormalization group study

We study magic-angle graphene with a small uniaxial strain at integer fillings using density-matrix renormalization group (DMRG), in which the Hartree-Fock study has reported a new type of ground state with momentum-modulated intervalley coherence. Unlike the Kramers intervalley coherent state (K-IVC), this state is time-reversal invariant but breaks moire translation symmetry with an "incommensurate Kekule spiral" (IKS) order at the microscopic graphene scale. In this work, we confirm the presence of the IKS order in the DMRG ground state, with its properties in good agreement with the Hartree-Fock predictions. We also find that, even in the absence of strain, such order is a strong candidate in the low-energy manifold of states, which closely competes with the valley-polarized order favored by Hartree-Fock numerics. This result suggests an expanded view in the phase diagram of twisted bilayer graphene.