Twist-tuned quantum criticality in moiré bilayer graphene

Abstract

We argue that moiré bilayer graphene at charge neutrality hosts a continuous semimetal-to-insulator quantum phase transition that can be accessed experimentally by tuning the twist angle between the two layers. For small twist angles near the first magic angle, the system realizes a Kramers intervalley-coherent insulator, characterized by circulating currents and spontaneously broken time reversal and U(1) valley symmetries. For larger twist angles above a critical value, the spectrum remains gapless down to the lowest temperatures, with a fully symmetric Dirac semimetal ground state. Using self-consistent Hartree-Fock theory applied to a realistic model of twisted bilayer graphene, based on the Bistritzer-MacDonald Hamiltonian augmented by screened Coulomb interactions, we find that the twist-tuned quantum phase transition is continuous. We argue that the quantum critical behavior belongs to the relativistic Gross-Neveu-XY universality class, and we characterize it through an effective field theory analysis. Our theoretical predictions can be directly tested using current experimental setups incorporating the recently developed quantum twisting microscope.

7+2 pages, 4+2 figures; v2: internal screening effects incorporated

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Cited by in corpus (6)

• Angle-Tuned Gross-Neveu Quantum Criticality in Twisted Bilayer Graphene: A Quantum Monte Carlo Study
• Relativistic Mott transitions and finite-temperature effects of quantum criticality in Dirac semimetals
• Strong-coupling superconductivity near Gross-Neveu quantum criticality in Dirac systems
• Superconductivity of Incoherent Electrons near the Relativistic Mott Transition in Twisted Dirac Materials
• Mean-field Modelling of Moiré Materials: A User's Guide with Selected Applications to Twisted Bilayer Graphene
• Dirac quantum criticality in twisted double bilayer transition metal dichalcogenides