Quantum-Critical Dirac Plasma in Supermoiré Lattices

Electronic correlations are a cornerstone of condensed-matter physics, often giving rise to intriguing quantum phases. The Dirac plasma, governed by electron-hole interactions at the charge neutrality point of graphene, behaves like a quantum-critical fluid, akin to the strongly correlated electrons in high-temperature superconductors.

In this presentation, we discuss the Dirac plasma within supermoiré lattices, where graphene is encapsulated between two hexagonal boron nitride (hBN) crystals. The strength of electronic correlations is modulated by varying the moiré twist angles. At zero magnetic field, the resistivity of the graphene supermoiré lattice becomes temperature-independent, saturating at approximately 1 kΩ above 150 K—a hallmark of the quantum-critical regime. Within this regime, the magnetoresistance (MR) increases linearly with the magnetic field, and its magnitude is strongly influenced by the moiré twist angles. By contrast, the MR of non-encapsulated graphene/hBN moiré superlattices remains unaffected by twist angles. Furthermore, the linear MR demonstrates temperature-independent behavior across a wide range (150 K to 300 K).

Our findings uncover a novel phenomenon in the quantum-critical regime: carrier density fluctuations driven by electronic correlations suppress the MR effect. This stands in sharp contrast to the traditional diffusive regime, where density fluctuations caused by charge impurities enhance the MR effect.