Abstract
Since the discovery of unconventional correlated insulators and superconductivity in magic-angle twisted bilayer graphene (TBG), graphene-based moiré systems have emerged as a major arena for correlated physics, hosting phenomena including ferromagnetism, fractional Chern insulator states, and, more recently, fractional quantum anomalous Hall effects. The field has moved towards increasingly elaborate structures, from the original TBG platform to twisted TMDCs and multilayer graphene moiré stacks.
Here, we report a novel and theoretically more tractable monolayer graphene system: double-aligned monolayer hBN/monolayer graphene heterostructures. We observe an exotic strong-correlation phenomenon: integer doping, in which pristine graphene acquires doping solely through the moiré reconstruction with hBN, and this doping is locked to an integer number of electrons or holes per moiré unit cell. This quantized doping can be electrically tuned between n-type and p-type regimes, acting as a novel discrete ferroelectricity. Scanning Tunneling Microscopy (STM) reveals that the moiré reconstruction transforms from a triangular to a hexagonal lattice upon switching, evidencing a phase transition where structural and electronic degrees of freedom are intricately intertwined. These observations originate from a network of pseudo-Landau levels (PLLs) that yields k-space flat bands and organizes into a real-space array of quantum dots. The gate-induced structural phase transition reconfigures the PLL distribution, thereby enabling the electrical switching of electronic states and realizing a coupled structural-electronic phase transition.
Biography
Dr Zihao Wang is a Senior Research Fellow and PI at the Institute for Functional Intelligent Materials (I-FIM), National University of Singapore. He received his PhD from the National Graphene Institute, University of Manchester in 2020, supervised by Nobel Laureate Prof. Sir Konstantin Novoselov, and continued his research with Prof. Novoselov upon relocating to Singapore. Since establishing his group in 2024, supported by the Young Individual Research Grant, his research has focused on moiré physics and strongly correlated phenomena in graphene heterostructures, combining transport measurements, scanning tunnelling microscopy, and atomic force microscopy. He was named to the Forbes 30 Under 30 Asia 2024 list.
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