Symmetry and topology of quasiparticles and their bound states in correlated insulators - Livestream

In this talk, I explore two examples of how the symmetry of a microscopic lattice or topoogy of an underlying non-interacting band structure can be imprinted in the excitations of strongly-correlated insulators. First, I show that previously-unnoticed crystal symmetry constraints drastically alter the understanding of Ising quantum criticality in the quasi-1D magnetic insulator CoNb2O6, resolving decade-old puzzles related to the dispersion of confined `kinks’ in the ordered phase and the decay of spin-flip quasiparticles in the paramagnetic phase [1]. Turning next to the correlated quantum anomalous Hall insulator recently observed in twisted bilayer graphene near the magic angle, I show that this state supports stable, weakly-dispersing flat bands of neutral bosonic excitons with substantial Berry curvature [2], and  argue that these can under certain conditions form a new hierarchy of bosonic  fractional quantum Hall liquids [3].

Speaker: Siddharth Parameswaran, Univ. of Oxford