The Magic Family of Twisted Graphene Superlattices

Since the discovery of magic-angle twisted bilayer graphene (MATBG), new types of moiré superlattices have been investigated to study strongly correlated and topologically nontrivial phenomena. Several interesting states, including but not limited to correlated insulators, quantized anomalous Hall states, ferromagnetism, and correlated Chern insulators, have been observed in various moiré materials. However, during the first few years, superconductivity was reproducibly seen only in MATBG. More recently, magic-angle twisted trilayer graphene (MATTG) has shown robust superconductivity and correlated states with an additional knob for electric displacement field tunability. Interestingly, MATBG and MATTG, which are the only robust moiré superconductors known to date, are part of a hierarchy of magic-angle graphene systems exhibiting a series of twist angles for different number of twisted layers. In this talk, I will introduce the physics behind MATTG in relation to the magic-hierarchy, and its striking behaviors including strong coupling superconductivity and large Pauli limit violation. I will also discuss our current understanding about the correlated states in this system, and present some of our most recent progress on this topic.