Layer-coherent phase in double-layer graphene at ν1=ν2=0

In the recent advancement in graphene heterostructures, it is possible to create a double-layer tunnel decoupled graphene system that has a strong interlayer electronic interaction. In this work, we restrict the parameters in the low energy effective Hamiltonian using simple symmetry arguments. Then, we study the ground state of this system in the Hartree-Fock approximation at ${\ensuremath{\nu}}₁^{}={\ensuremath{\nu}}₂^{}=0$. In addition to the phases found in monolayer graphene, we found an existence of layer-coherent phase which breaks the layer $U(1)$ symmetry. At nonzero Zeeman coupling strength $({E}_z)$, this layer-coherent state has a small magnetization that vanishes when ${E}_z$ tends to zero. We discuss the bulk gapless modes using the Goldstone theorem. We also comment on the edge structure for the layer-coherent phase.