Symmetry enriched U(1) quantum spin liquids

TL;DR

This paper classifies three-dimensional $U(1)$ quantum spin liquids with various symmetries, revealing 168 distinct phases and providing a framework for understanding their bulk and surface properties.

Contribution

It offers a comprehensive classification of symmetry-enriched $U(1)$ quantum spin liquids, including new states and a framework for analyzing their anomalies and surface phenomena.

Findings

Identified 15 distinct spin liquids with time reversal and $SO(3)$ symmetry.

Refined classification to 168 phases considering symmetry coupling and surface properties.

Discovered 38 anomaly-free and 37 anomalous spin liquids with time reversal and $Z_2$ symmetry.

Abstract

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). We first 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 provide a general framework to classify symmetry enriched $U(1)$ quantum spin liquids for a large class of symmetries. As a more complex example, we discuss $U(1)$ quantum spin liquids with time reversal and $Z_2$ symmetries in detail. Based on the properties of the bulk excitations, we find there are 38 distinct such spin liquids that are anomaly-free. There are also 37 anomalous $U(1)$ quantum spin liquids with this symmetry. Finally, we briefly discuss the classification of $U(1)$ quantum spin liquids enriched by some other symmetries.