Global Phase Diagram of the Normal State of Twisted Bilayer Graphene

We investigate the full doping and strain-dependent phase diagram of the normal state of magic-angle twisted bilayer graphene (TBG). Using comprehensive Hartree-Fock calculations, we show that at temperatures where superconductivity is absent the global phase structure can be understood based on the competition and coexistence between three types of intertwined orders: a fully symmetric phase, spatially uniform flavor-symmetry-breaking states, and an incommensurate Kekule spiral (IKS) order. For small strain, the IKS phase, recently proposed as a candidate order at all nonzero integer fillings of the moire unit cell, is found to be ubiquitous for noninteger doping as well. We demonstrate that the corresponding electronic compressibility and Fermi surface structure are consistent with the cascade physics and Landau fans observed experimentally. This suggests a unified picture of the phase diagram of TBG in terms of IKS order.

Automated summary

We investigate the phase diagram of twisted bilayer graphene (TBG) in the normal state, considering doping and strain dependence. Our comprehensive calculations reveal the competition and coexistence of three intertwined orders: a fully symmetric phase, flavor-symmetry-breaking states, and an incommensurate Kekule spiral (IKS) order. The IKS order is found to be ubiquitous for noninteger doping as well, consistent with experimental observations of electronic compressibility and Fermi surface structure. This study suggests a unified picture of the phase diagram in terms of IKS order.