Xie Chen – California Institute of Technology
Title: Fracton and Chern-Simons Theory

Abstract: Fracton order describes the peculiar phenomena that point excitations in certain strongly interacting systems either cannot move at all or can only move in a lower dimensional sub-manifold. It has recently been discovered in various lattice models, tensor gauge theories, etc. In this talk, we discuss how another powerful field theory framework — the 2+1D Chern-Simons (CS) gauge theory — can be used to provide new insight and explore new possibilities in 3+1D fracton order. 2+1D U(1) gauge theories with a CS term provide a simple and complete characterization of 2+1D Abelian topological orders. To study 3+1D fracton order, we extend the theory by taking the number of component gauge fields to be infinity. In the simplest case of infinite-component CS gauge theory, different components do not couple to each other and the theory describes a decoupled stack of 2+1D fractional Quantum Hall systems with quasi-particles moving only in 2D planes — hence a fractonic system. More interestingly, we find that when the component gauge fields do couple through the CS term, more varieties of fractonic orders are possible. For example, they may describe foliated fractonic systems which extends the framework found in exactly solvable models. Moreover, we find examples which lie beyond the foliation framework, characterized by 2D excitations of infinite order and braiding statistics that are not strictly local.

Speaker Bio: Xie Chen is a Professor of Theoretical Physics at the California Institute of Technology. Dr. Chen obtained her Ph.D. degree from MIT in 2012 and was a Miller research fellow at the University of California, Berkeley before joining Caltech in 2014. Dr. Chen is a condensed matter theorist studying emergent phenomena in strongly interacting quantum many-body systems. She received the New Horizons in Physics Prize from the Breakthrough Foundation in 2020 and was named a Simons Investigator in 2021.

(This event is virtual and can be watched at the link below or in BRIM/AMPL 311)