Neel to staggered dimer order transition in a generalized honeycomb lattice Heisenberg model

TL;DR

This paper investigates a phase transition in a honeycomb lattice spin-1/2 Heisenberg model, revealing a strong first-order transition from Neel to staggered dimer order driven by four-spin interactions, with implications for understanding quantum phase transitions.

Contribution

It demonstrates a first-order Neel to staggered dimer transition in a honeycomb lattice model using multiple theoretical and numerical methods, highlighting the role of Z(3) vortices.

Findings

First-order transition between Neel and staggered dimer states.

Disordering Z(3) vortices does not induce magnetic order.

Dimer and Neel orders are independent in this model.

Abstract

We study a generalized honeycomb lattice spin-1/2 Heisenberg model with nearest-neighbor antiferromagnetic 2-spin exchange, and competing 4-spin interactions which serve to stabilize a staggered dimer state which breaks lattice rotational symmetry. Using a combination of quantum Monte Carlo numerics, spin wave theory, and bond operator theory, we show that this model undergoes a strong first-order transition between a Neel state and a staggered dimer state upon increasing the strength of the 4-spin interactions. We attribute the strong first order character of this transition to the spinless nature of the core of point-like Z(3) vortices obtained in the staggered dimer state. Unlike in the case of a columnar dimer state, disordering such vortices in the staggered dimer state does not naturally lead to magnetic order, suggesting that, in this model, the dimer and Neel order parameters should be thought of as independent fields as in conventional Landau theory.