Moiré Engineering of Magnetoresistance in the Quantum-Critical Regime of Graphene Supermoiré Lattice

The Dirac plasma, an electron-hole (e-h) plasma of Dirac fermions at the charge-neutrality point of graphene, behaves as a hydrodynamic quantum critical fluid, similar to strongly correlated electrons in high-temperature superconductors [1-2]. However, the hydrodynamic transport of Dirac plasma through moiré potential is not well understood. In this talk, I present our investigation of the Dirac plasma in monolayer graphene encapsulated between two hBN crystals, where the strength of the moiré potential is controlled using our rotation alignment technique [3]. At zero magnetic field, the moiré potentials result in a slight temperature dependence, with resistivity saturating at ~1 kohm. This behaviour can be attributed to the onset of the quantum-critical regime, where the scattering is dominated by the Planckian frequency (~K_BT/<i>h</i>). When a magnetic field is applied, all moiré systems show a linear increase in resistivity with the magnetic field, but the magnitude varies significantly based on the moiré twist angels. In contrast, the magnetoresistance (MR) in non-encapsulated graphene/hBN moiré superlattice remains unchanged with different moiré twist angels. We developed a quantum effective medium theory (EMT) to show that in the hydrodynamic regime, moiré potentials dominate carrier density fluctuation, leading to modulation of the MR effect. While in the traditional diffusive regime, charge impurities dominate the carrier density fluctuation, masking the effect of the moiré potential on MR. Our work demonstrates a two-dimensional system based on the hydrodynamic regime of graphene supermoiré lattices, offering robust, stable, and highly sensitive magnetic field detection. This system shows promise for the next generation of 2D magnetic field sensor. This work is supported by the MOE Singapore Tier 1 (A-8001967-00-00), Tier 2 (MOE-T2EP50120-0015), the NRF-ISF Singapore joint program (NRF2020-NRF-ISF004-3518) and the A*STAR under its MTC Young Investigator Research Grant (YIRG) (Grant No. M23M7c0124).<br/><br/>References<br/><br/>[1] Crossno, J. et al. Science 351, 1058–1061 (2016).<br/>[2] Ku, M. J. H. et al. Nature 583, 537–541(2020).<br/>[3] Hu J. X., et al. Nat Commun 14, 4142 (2023).