# SU(4) topological RVB spin liquid on the square lattice

## TL;DR

This paper constructs and analyzes a topological SU(4) spin liquid state on a square lattice using PEPS, demonstrating its topological nature and relevance to ultracold atom experiments.

## Contribution

It generalizes the SU(2) RVB state to SU(4), introduces a family of such states, and provides evidence of their topological spin liquid properties.

## Key findings

- Longer-range bonds break gauge symmetry from U(1) to Z2.
- Evidence of topological order from entanglement entropy and modular matrices.
- Relevance to ultracold atom experimental systems.

## Abstract

We generalize the construction of the spin-1/2 SU(2) Resonating Valence Bond (RVB) state to the case of the self-conjugate $\bf 6$-representation of SU(4). As for the case of SU(2) [J-Y. Chen and D. Poilblanc, Phys. Rev. B $\textbf{97}$, 161107(R) (2018)], we use the Projected Entangled Pair State (PEPS) formalism to derive a simple (two-dimensional) family of generalized SU(4) RVB states on the square lattice. We show that, when longer-range SU(4)-singlet bonds are included, a local gauge symmetry is broken down from U(1) to $\mathbb{Z}_2$, leading to the emergence of a short-range spin liquid. Evidence for the topological nature of this spin liquid is provided by the investigation of the Renyi entanglement entropy of infinitely-long cylinders and of the modular matrices. Relevance to microscopic models and experiments of ultracold atoms is discussed.