Failure of Nielsen-Ninomiya Theorem and Fragile Topology in Two-Dimensional Systems with Space-Time Inversion Symmetry: Application to Twisted Bilayer Graphene at Magic Angle

Abstract

A new theory reveals the topological origin of the mismatch between the number of left- and right-handed Dirac quasiparticles in twisted bilayer graphene, which is a step toward identifying new topological phases of matter.