Flavor Symmetry and Competing Orders in Bilayer Graphene

Understand

We analyze competition between different ordered states in bilayer graphene (BLG).

• Combining arguments based on SU(4) spin-valley flavor symmetry with a mean field analysis, we identify the lowest energy state with the anomalous Hall insulator (AHI).
• This state is an SU(4) singlet excitonic insulator with broken time reversal symmetry, exhibiting quantized Hall effect in the absence of external magnetic field.
• Applied electric field drives an Ising-type phase transition, restoring time reversal symmetry.