Condensed Matter Seminar: Liujun Zou, Harvard - “Symmetry enriched U(1) quantum spin liquids”

Event time: 
Monday, October 16, 2017 - 2:00pm to 3:00pm
Sloane Physics Laboratory (SPL), 52 See map
217 Prospect Street
New Haven, CT 06511
Event description: 

We classify and characterize three dimensional $U(1)$ quantum spin liquids (deconfined $U(1)$ gauge theories) with global symmetries. These spin liquids have an emergent gapless photon and emergent electric/magnetic excitations (which we assume are gapped). In this talk I will mainly discuss in great detail the case with time reversal and $SO(3)$ spin rotational symmetries. We find there are 15 distinct such quantum spin liquids based on the properties of bulk excitations. We show how to interpret them as gauged symmetry-protected topological states (SPTs). Some of these states possess fractional response to an external $SO(3)$ gauge field, due to which we dub them “fractional topological paramagnets”. We identify 11 other anomalous states that can be grouped into 3 anomaly classes. The classification is further refined by weakly coupling these quantum spin liquids to bosonic Symmetry Protected Topological (SPT) phases with the same symmetry. This refinement does not modify the bulk excitation structure but modifies universal surface properties. Taking this refinement into account, we find there are 168 distinct such $U(1)$ quantum spin liquids. After this warm-up we briefly describe a general framework to classify symmetry enriched $U(1)$ quantum spin liquids for a large class of symmetries.