Abstract

Quantization stands as a defining hallmark of low-dimensional physics and powers many of today's most cutting-edge technologies. In zero-dimensional systems, quantum dots harness discrete states to realize spin/charge qubits—the building blocks of quantum computers. At the macroscopic (μm) scale, the only quantized state that has found practical application is the quantized conductance arising from the quantum Hall effect, which has been adopted worldwide as the international resistance standard. Here we report a novel macroscopic quantized state—integer doping—which demonstrates doping with a quantized integer number of electrons (or holes) per moiré plaquette in an hBN-encapsulated double aligned monolayer graphene device1. This integer doping is gate-tunable, flipping between positive and negative integers (e.g., +2 to -4). Such gate-tunable electronic phase transition couples to a novel structural phase transition (triangular-to-hexagonal) that can be directly visualized by AFM and STM in fabricated devices, enabled by using monolayer hBN instead of bulk BN for top encapsulation. Underlying this novel integer-doping phase transition is the charge localization of the strain-induced flat bands formed by moiré reconstruction, significantly enhanced by monolayer hBN. Being a first-order phase transition, it can be triggered instantaneously by gate voltage. The resulting abrupt hysteresis—set by discrete, quantized carrier states rather than remnant polarization—offers advantages over conventional ferroelectric hysteresis for integrated circuit applications. Its instantaneous carrier-set switching between discrete states are directly connected to digital bits and physically anchors the decision boundary—delivering fixed thresholds, large noise margins, read/write decoupling, and a simple single-gate periphery.

Biography

Dr. Zihao Wang is a Senior Research Fellow and group 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 nano electronics 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.