Yonglong Xie

When two graphene layers are stacked with a “magic angle” of 1.1 degrees, the resulting periodic moiré lattice gives rise to quantum states, such as unconventional superconductivity, that are unattainable in monolayer graphene.

This groundbreaking discovery in 2018 rapidly elevated moiré materials to the forefront of condensed matter physics. However, it also introduced a host of unresolved questions: How do these quantum states emerge? Are there other hidden quantum phases yet to be discovered? Taking these as a starting point, Yonglong Xie launched a series of studies using scanning probe microscopy.

His spectroscopic measurements of magic-angle twisted bilayer graphene (MATBG) revealed that across all doping levels, electron-electron interactions dominate the system’s energy landscape. He subsequently discovered the long-sought fractional Chern insulator in MATBG, a state that realizes the fractional quantum Hall effect without a large external magnetic field, unlocking new possibilities for topological quantum devices.

While it was previously believed that stacking additional layers atop a moiré lattice would create supermoiré lattices that disrupt its periodicity, his research overturned this view. He demonstrated that supermoiré lattices not only reveal hidden properties of moiré systems but also serve as a powerful tool to engineer and control emergent quantum phenomena.

Furthermore, while theoretical studies predict that non-Abelian anyons may arise in a special class of fractional Chern insulators, those discovered in moiré systems to date have not exhibited non-Abelian characteristics. Yonglong is currently searching for non-Abelian anyons in these materials using scanning probe microscopy.