Instability of isolated triplet excitations on the Shastry-Sutherland lattice (SSL)

TL;DR

This paper proves that isolated triplet excitations on the Shastry-Sutherland lattice become unstable below a critical coupling, with implications for the magnetic compound SrCu₂(BO₃)₂.

Contribution

It establishes the critical coupling value for triplet instability on the SSL, providing insight into the magnetic properties of related materials.

Findings

Triplet excitations are unstable for alpha < 2.0

The critical coupling alpha_c is approximately 2.0

SrCu₂(BO₃)₂ has a coupling alpha* of about 1.48

Abstract

Configurations of singlets and triplets on the SSL have been proposed in the literature as variational ground states of the Shastry-Sutherland model at fixed magnetization M. We prove, that isolated triplet excitations on the SSL are unstable if the coupling alpha falls below a critical value alpha_c=2.0 (approx.). The instability should be visible in the compound SrCu_2(BO_3)_2 where a coupling alpha^*=1.48 is realized.