(a) Phase diagram in the t–h plane for J_ab = −0.2, ε = 0.5. (b) Ground-state phase diagram in the ε–h plane for J_ab = −0.2. FP refers to fully polarized. The QMC simulations are performed at t = 0.02 (corresponds to T ∼ 50 mK for YbAlO₃) with system size 20 × 20 × 128 to ensure the convergence to the ground state. The error bar of the phase boundary data is about 0.02, which is smaller than the symbol size. The extrapolations are shown as the dashed lines.