Topology-driven deconfined quantum criticality in magnetic bilayers

TL;DR

This paper demonstrates how topological interactions between layers in magnetic bilayers can induce a deconfined quantum critical point, revealing novel critical behavior driven by emergent gauge fields and topological terms.

Contribution

It introduces a topological Chern-Simons coupling between layers that modifies the critical behavior of the Nel-VBS transition in antiferromagnets.

Findings

Topological current-current interaction influences quantum critical scaling.

Non-universal power-law divergence of correlation length observed.

Berezinskii-Kosterlitz-Thouless divergence near criticality.

Abstract

Two-dimensional quantum antiferromagnets are believed to host phases of matter whose excitations are more fundamental than those of the ordered phases. When combining two such spin systems in a bilayer, strong interaction between the emergent excitations can produce phases not realized in either of its subsystems. We show that the critical fluctuations of a two-dimensional spin liquid state can induce a deconfined quantum critical point in a proximate antiferromagnet. The most relevant coupling between the associated effective field theories is given by a mixed Chern-Simons term of the emergent gauge fields in each layer. This describes a topological current-current interaction. In contrast to the local spin-spin interaction, it strongly modifies the renormalization group flow of the theory describing the N\'eel-valence-bond-solid transition of the antiferromagnet. In particular, the protected coupling constant associated with it implies non-trivial quantum critical scaling characterized by a non-universal power-law divergence of the correlation length in the critical domain and Berezinskii-Kosterlitz-Thouless divergence approaching it.