The two dimensional Antiferromagnetic Heisenberg model with next nearest neighbour Ising exchange

TL;DR

This paper studies a 2D antiferromagnetic Heisenberg model with next nearest neighbor Ising interactions, revealing phase transitions and potential deconfined quantum critical points through numerical analysis.

Contribution

It introduces two generalizations of the model that demonstrate a transition from first to second order, providing candidate examples of deconfined quantum criticality.

Findings

Large next nearest neighbor coupling leads to striped phase.

Transition from first to second order in generalized models.

Estimated quantum critical exponent β ≈ 0.25.

Abstract

We have considered the $S=1/2$ antiferromagnetic Heisenberg model in two dimensions, with an additional Ising \nnn interaction. Antiferromagnetic \nnn interactions will lead to frustration, and the system responds with flipping the spins down in the $xy$ plane. For large next nearest neighbour coupling the system will order in a striped phase along the z axis, this phase is reached through a first order transition. We have considered two generalizations of this model, one with random \nnn interactions, and one with an enlarged unit cell, where only half of the atoms have \nnn interactions. In both cases the transition is softened to a second order transition separating two ordered states. In the latter case we have estimated the quantum critical exponent $\beta \approx 0.25$. These two cases then represent candidate examples of deconfined quantum criticality.