Antiferromagnets on the Shastry-Sutherland lattice have attracted lots of research interest due to the possible existence of deconfined criticality. In the present work, we study the $J_1\text{−}{J}_2\text{−}{J}_r$ model using variational Monte Carlo (VMC) method, where $J_1, J_2$, and $J_r$ stand for the nearest-neighbor, next-nearest-neighbor, and ring exchange interactions, respectively. An empty plaquette (EP) phase with spontaneous mirror symmetry breaking is reproduced. However, the EP phase in the VMC approach is $Z_2$ deconfined and have Majorana-type gapless spinon excitations, which is qualitatively different from the EP phase in literature. The central observation of the present study is the gapless $Z_2$ Quantum spin liquid phase resulting from the competition between the EP phase, the full plaquette (FP) phase and the antiferromagnetic Néel phase. While the phase transition from the $Z_2$ QSL phase to the EP phase is likely of Landau-Ginzburg type, the continuous transitions to the confined FP and Néel phases are exotic and need to be further explored.

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• Magnetism
• Quantum spin liquid
• Strongly correlated systems
• Monte Carlo methods