On the precise boundary of the Néel antiferromagnetic phase in the Shastry-Sutherland model

The ground state phase diagram of the Shastry-Sutherland model remains controversial. In particular, the nature of the transition between the plaquette valence bond solid (PVBS) phase and the Néel antiferromagnetic (AFM) phase is still under debate. While some studies suggest a direct transition between the two phases, others propose the existence of a narrow intermediate quantum spin liquid regime. To address this issue, we perform large-scale Density Matrix Renormalization Group calculations to determine the Néel AFM phase boundary in the Shastry-Sutherland model. By applying staggered boundary pinning fields and directly measuring the bulk staggered magnetization, and through systematic extrapolations with respect to truncation error as well as careful finite-size scaling, we find that the staggered magnetization remains finite across the controversial region 0.78 ≲ J 1 / J 2 ≤ 0.81, which was suggested to host a quantum spin liquid phase in some studies. Together with the previously established consensus placing the PVBS phase boundary at J 1 / J 2 ≈ 0.78, these results, within the resolution of the present calculations, provide evidence against the existence of an intermediate quantum spin liquid phase and support a direct PVBS-Néel AFM transition in the Shastry-Sutherland model.