Today, the team of Pablo Jarillo-Herrero and Yuan Cao at MIT published amazing results again today, performing both thermodynamic and transport measurements to study symmetry-breaking many-body ground states and the non-trivial topology of magic-angle twisted bilayer graphene (MATBG).

    This research is based on a 2018 study in which the same team - Pablo Jarillo-Herrero and Yuan Cao's team at MIT - discovered new electronic states in ~1.1° magic-angle twisted bilayer graphene for a simple insulator-to-superconductor transition, opening the unconventional superconductor research.

    The new study directly observes symmetry breaking as “pinning” of the chemical potential of the Moiré superlattice at all integer fills, confirming the importance of Hund coupling in the many-body ground state. In addition, the researchers explored the topological properties of MATBG by measuring the energy gaps corresponding to the Chern insulating states, where the Chern insulating states have Chern numbers of 3, 2, and 1, and filling factors of 1, 2, and 3, which are consistent with the symmetry breaking in the Hofstadter butterfly spectrum of MATBG.

    The team also tested the resistivity and chemical potential of magic-angle graphene simultaneously, obtaining a temperature-dependent charge diffusivity in the singlet metal state, which has only been found in ultracold atoms before.

    Overall, the researchers demonstrate the power of MATBG as a “playground” to explore exotic physics in a highly tunable and experimentally adressible system. The study, in the words of the authors, brings us “one step closer to a unified framework for understanding interactions in the topological bands of MATBG, with and without a magnetic field.”

    Yuan Cao was admitted to the School of the Gifted Young of the University of Science and Technology of China (USTC) in 2010, and was selected to the "Yan Jizi Physics Honor’s Class". On March 5, 2018, Nature published two back-to-back papers on graphene with Yuan Cao as the first author. The USTC SGY graduate and PhD student at the Massachusetts Institute of Technology discovered that when two layers of parallel graphene are stacked at a delicate angle of about 1.1°, a miraculous superconducting effect occurs. This discovery was an international sensation and directly opened up a new field of condensed matter physics. In 2018, Cao Yuan was selected as the youngest person in the list of "30 under 30" in the field of science and technology by Forbes China at the age of 22.

Translated by SHI Kexin.