Emergent Spin Liquids in the Hubbard Model on the Anisotropic Honeycomb Lattice

TL;DR

This paper investigates the Hubbard model on an anisotropic honeycomb lattice, revealing the emergence of various insulating spin-liquid phases at intermediate couplings, including both gapless and gapped types, with the gapped phase dominating at high anisotropy.

Contribution

It introduces the discovery of multiple spin-liquid phases in the Hubbard model on an anisotropic honeycomb lattice using mean-field and slave-rotor methods, highlighting the prevalence of a gapped spin liquid at high anisotropy.

Findings

Identification of spin-liquid phases at intermediate couplings.

Gapped spin liquid dominates at large hopping anisotropies.

Phase diagram includes semi-metallic, insulating, and antiferromagnetic phases.

Abstract

We study the repulsive Hubbard model on an anisotropic honeycomb lattice within a mean-field and a slave-rotor treatment. In addition to the known semi-metallic and band-insulating phases, obtained for very weak interactions, and the anti-ferromagnetic phase at large couplings, various insulating spin-liquid phases develop at intermediate couplings. Whereas some of these spin liquids have gapless spinon excitations, a gapped one occupies a large region of the phase diagram and becomes the predominant phase for large hopping anisotropies. This phase can be understood in terms of weakly-coupled strongly dimerized states.