Exact results for the star lattice chiral spin liquid

TL;DR

This paper provides exact analytical results for the phase diagram and ground state degeneracy of the star lattice Kitaev model, revealing its chiral spin liquid nature and topological properties.

Contribution

It introduces an exact fermionic representation of the star lattice Kitaev model, elucidates its phase diagram, and demonstrates non-Abelian ground state degeneracy.

Findings

The model exhibits a spherical phase diagram with Abelian and non-Abelian phases.

The Abelian phase is inherited from fermionic vacua related to toric code states.

The model has a three-fold non-Abelian ground state degeneracy on a torus.

Abstract

We examine the star lattice Kitaev model whose ground state is a a chiral spin liquid. We fermionize the model such that the fermionic vacua are toric code states on an effective Kagome lattice. This implies that the Abelian phase of the system is inherited from the fermionic vacua and that time reversal symmetry is spontaneously broken at the level of the vacuum. In terms of these fermions we derive the Bloch-matrix Hamiltonians for the vortex free sector and its time reversed counterpart and illuminate the relationships between the sectors. The phase diagram for the model is shown to be a sphere in the space of coupling parameters around the triangles of the lattices. The abelian phase lies inside the sphere and the critical boundary between topologically distinct Abelian and non-Abelian phases lies on the surface. Outside the sphere the system is generically gapped except in the planes where the coupling parameters are zero. These cases correspond to bipartite lattice structures and the dispersion relations are similar to that of the original Kitaev honeycomb model. In a further analysis we demonstrate the three-fold non-Abelian groundstate degeneracy on a torus by explicit calculation.