The Fate of the Two-Magnon Bound State in the Heisenberg Antiferromagnet

TL;DR

This paper investigates the behavior of two-magnon bound states in the Heisenberg antiferromagnet, showing they disappear into the continuum before reaching the isotropic limit, using series expansion calculations.

Contribution

It provides the first detailed series expansion analysis confirming the disappearance of bound states prior to the isotropic limit, supporting earlier spin-wave predictions.

Findings

Two-magnon bound states vanish into the continuum before the isotropic limit.

Series expansion results confirm earlier spin-wave predictions.

Bound states do not survive at the isotropic Heisenberg point.

Abstract

The energy spectrum of the two-magnon bound states in the Heisenberg-Ising antiferromagnet on the square lattice are calculated using series expansion methods. The results confirm an earlier spin-wave prediction of Oguchi and Ishikawa, that the bound states vanish into the continuum before the isotropic Heisenberg limit is reached.