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Universal Fermi-surface anisotropy renormalization for interacting Dirac fermions with long-range interactions

Recent experimental and numerical evidence suggest an intriguing universal relationship between the Fermi surface anisotropy of the non-interacting parent two-dimensional electron gas and the strongly correlated composite Fermi liquid formed in a strong magnetic field close to half-filing. Inspired by these observations, we explore more generally the question of anisotropy renormalization in interacting 2D Fermi systems. Using a recently developed non-perturbative and numerically-exact projective quantum Monte Carlo simulation as well as other numerical and analytic techniques, only for Dirac fermions with long-range Coulomb interactions do we find a universal square-root decrease of the Fermi-surface anisotropy. For the half-filled composite Fermi liquid, this result is surprising since a Dirac fermion ground state was only recently proposed as an alternative to the usual HLR state. The importance of the long-range interaction, expected for Dirac systems, is also consistent with recent transport measurements. Our proposed universality can be tested in several anisotropic Dirac materials including graphene, topological insulators organic conductors, and magic-angle twisted bilayer graphene.