Gapped $Z_2$ spin liquid in the breathing kagome Heisenberg antiferromagnet

TL;DR

This paper introduces an improved RVB ansatz for the breathing kagome Heisenberg antiferromagnet that captures a gapped $Z_2$ topological spin liquid state, showing promising variational energies and topological order.

Contribution

It develops a simple, symmetry-preserving simplex RVB ansatz with quantum gate filtering, revealing a stable $Z_2$ topological order in the breathing kagome antiferromagnet.

Findings

The ansatz achieves good variational energies at various anisotropies.

It demonstrates persistent $Z_2$ topological order under quantum gate applications.

Suggests the $Z_2$ spin liquid as a competing ground state at large breathing anisotropy.

Abstract

We investigate the spin-1/2 Heisenberg antiferromagnet on the kagome lattice with breathing anisotropy (i.e. with weak and strong triangular units), constructing an improved simplex Resonating Valence Bond (RVB) ansatz by successive applications (up to three times) of local quantum gates which implement a filtering operation on the bare nearest-neighbor RVB state. The resulting Projected Entangled Pair State involves a small number of variational parameters (only one at each level of application) and preserves full lattice and spin-rotation symmetries. Despite its simple analytic form, the simplex RVB provides very good variational energies at strong and even intermediate breathing anisotropy. We show that it carries $Z_2$ topological order which does not fade away under the first few applications of the quantum gates, suggesting that the RVB topological spin liquid becomes a competing ground state candidate for the kagome antiferromagnet at large breathing anisotropy.