Strong interaction effects at a Fermi surface in a model for voltage-biased bilayer graphene

Monte Carlo simulation of a 2+1 dimensional model of voltage-biased bilayer graphene, consisting of relativistic fermions with chemical potentialμcoupled to charged excitations with opposite sign on each layer, has exposed noncanonical scaling of bulk observables near a quantum critical point found at strong coupling. We present a calculation of the quasiparticle dispersion relation E(k) as a function of exciton source j in the same system, employing partially twisted boundary conditions to boost the number of available momentum modes. The Fermi momentum kF and superfluid gap Δ are extracted in the j→0 limit for three different values of μ, and support a strongly interacting scenario at the Fermi surface with Δ ∼ O(μ). We propose an explanation for the observation μ < kF in terms of a dynamical critical exponent z < 1.