Hofstadter butterfly study published in Nature Physics

Our study of the strongly interacting Hofstadter butterfly in magic-angle twisted bilayer graphene was published in Nature Physics. Using an exceptionally clean sample, we measured electrical transport in a magnetic field and uncovered two striking phenomena. First, there is a cascade of Chern-insulator states that spontaneously enlarge the moiré unit cell, with a sequence of Chern numbers echoing those of their parent topological states. Second, we found fractional quantum Hall states with a counterintuitive twist—they weaken, rather than strengthen, as the magnetic field increases. Our theory reproduces the full cascade of charge-density-wave Chern insulators and uncovers new quantum geometric properties of the fractionalized states unique to the moiré superlattice. Congratulations to Minhao and all our co‑authors!