RQMP Research Seminar

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

Siddharth Ashok Parameswaran

University of Oxford

In this talk, I explore two examples of how the symmetry of a microscopic lattice or topology 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]. I will then change focus to the correlated quantum anomalous Hall insulator recently observed in twisted bilayer graphene near the magic angle, where I will discuss the topological properties [2] and many-body physics [3] of excitonic bound states.

References:
[1] M. Fava, R. Coldea, and S.A. Parameswaran, arXiv:2004.04169 (2020), to appear in PNAS.
[2] Y.H. Kwan, Y. Hu, S.H. Simon, and S.A. Parameswaran, arXiv:2003.11560 (2020).
[3] Y.H. Kwan, Y. Hu, S.H. Simon, and S.A. Parameswaran, arXiv:2003.11559 (2020).