Chiral spin liquid in a generalized Kitaev honeycomb model with $\mathbb{Z}_4$ 1-form symmetry

TL;DR

This paper investigates a generalized Kitaev honeycomb model with a $ ext{Z}_4$ one-form symmetry, revealing a gapped, topologically ordered chiral spin liquid with edge modes described by a free boson CFT and $ ext{U}(1)_{-8}$ topological order.

Contribution

It introduces a $ ext{Z}_4$ symmetric Kitaev model, analyzes its topological order and edge states, and connects it to a broader class of $ ext{Z}_N$ Kitaev models.

Findings

Model is gapped with short correlation length.

Supports chiral edge modes described by a free boson CFT.

Exhibits $ ext{U}(1)_{-8}$ topological order.

Abstract

We explore a large $N$ generalization of the Kitaev model on the honeycomb lattice with a simple nearest-neighbor interacting Hamiltonian. In particular, we focus on the $\mathbb{Z}_4$ case with isotropic couplings, which is characterized by an exact $\mathbb{Z}_4$ one-form symmetry. Guided by symmetry considerations and an analytical study in the single chain limit, on the infinitely long cylinders, we find the model is gapped with an extremely short correlation length. Combined with the $\mathbb{Z}_4$ one-form symmetry, this suggests the model is topologically ordered. To pin down the nature of this phase, we further study the model on both finite and infinitely long strips, where we consistently find a $c=1$ conformal field theory (CFT) description, suggesting the existence of chiral edge modes described by a free boson CFT. Further evidence is found by studying the dimer correlators on infinitely long strips. We find the dimer correlation functions show a power-law decay with the exponent close to 2 on the boundary of the strip, while decay much faster in the bulk. Combined with the topological entanglement entropy extracted from cylinder geometry, we identify the spin liquid is chiral and supports a $\mathrm{U}(1)_{-8}$ chiral topological order. A unified perspective for all $\mathbb{Z}_N$ type Kitaev models is also discussed.