Two-dimensional Valence Bond Solid (AKLT) states from $t_{2g}$ electrons

TL;DR

This paper proposes a physical realization of the 2D AKLT state using $t_{2g}$ electrons in multiorbital Mott insulators, demonstrating a phase transition to antiferromagnetic order and suggesting experimental detection methods.

Contribution

It introduces a feasible way to realize the spin-3/2 AKLT state on a honeycomb lattice through orbital physics, bridging theoretical models and experimental systems.

Findings

Phase transition from AKLT to Neel state with increasing Hund's coupling

DMRG simulations confirm the phase transition

Experimental signature includes protected free spins-1/2 at vacancies

Abstract

Two-dimensional AKLT model on a honeycomb lattice has been shown to be a universal resource for quantum computation. In this valence bond solid, however, the spin interactions involve higher powers of the Heisenberg coupling $(\vec{S}_i \cdot \vec{S}_j)^n$, making these states seemingly unrealistic on bipartite lattices, where one expects a simple antiferromagnetic order. We show that those interactions can be generated by orbital physics in multiorbital Mott insulators. We focus on $t_{2g}$ electrons on the honeycomb lattice and propose a physical realization of the spin-$3/2$ AKLT state. We find a phase transition from the AKLT to the Neel state on increasing Hund's rule coupling, which is confirmed by density matrix renormalization group (DMRG) simulations. An experimental signature of the AKLT state consists of protected, free spins-1/2 on lattice vacancies, which may be detected in the spin susceptibility.