Bilayer graphene: Domain walls, superlattices, and implications for transport

Bilayer graphene is made of two graphene monolayers which are Bernal stacked and have quadratic band touching. Applying a uniform electric field perpendicular to the bilayer results in a gap - but the measured gap is always much smaller than the expected value. This motivates us to explore modulations of the electric field and chemical potential as a first step in thinking about disorder physics. Interestingly, a sign flip in the electric field is shown to induce localized "domain wall" fermions, which form a tunable Tomonaga-Luttinger liquid once interactions are taken into account. A superlattice of such domain walls is shown to exhibit excitations which take the form of anisotropic massless Dirac fermions which are expected to be perturbatively stable against interactions. Chemical potential modulations are also shown to generate such anisotropic massless Dirac fermion states. Finally, we consider disordered configurations of such modulations within a numerical tight binding approach and find evidence of subgap states in the biased bilayer - this might partially help to account for the experimentally observed low temperature and low frequency transport.