Coupled Cluster Treatment of the Shastry-Sutherland Antiferromagnet

TL;DR

This paper uses high-order coupled cluster methods to analyze the zero-temperature phases of the Shastry-Sutherland antiferromagnet, predicting phase transition points and identifying an intermediate disordered phase.

Contribution

It provides new high-precision predictions for phase transition points and confirms the existence of an intermediate disordered phase in the model.

Findings

Orthogonal-dimer state becomes groundstate at J2/J1 ~ 1.477

Critical point for Nél order disappearance is between 1.14 and 1.39

Spiral phase does not become the groundstate for any J2 value

Abstract

We consider the zero-temperature properties of the spin-half two-dimensional Shastry-Sutherland antiferromagnet by using a high-order coupled cluster method (CCM) treatment. We find that this model demonstrates various groundstate phases (N\'{e}el, magnetically disordered, orthogonal dimer), and we make predictions for the positions of the phase transition points. In particular, we find that orthogonal-dimer state becomes the groundstate at ${J}^{d}_2/J_1 \sim 1.477$. For the critical point $J_2^{c}/J_1$ where the semi-classical N\'eel order disappears we obtain a significantly lower value than $J_2^{d}/J_1$, namely, ${J}^{c}_2/J_1$ in the range $[1.14, 1.39]$. We therefore conclude that an intermediate phase exists between the \Neel and the dimer phases. An analysis of the energy of a competing spiral phase yields clear evidence that the spiral phase does not become the groundstate for any value of $J_2$. The intermediate phase is therefore magnetically disordered but may exhibit plaquette or columnar dimer ordering.