We investigate the spin-$1/2$ $J_1–J_2$ triangular-lattice Heisenberg antiferromagnet in a magnetic field by combining large-scale density matrix renormalization group (DMRG) simulations with self-consistent spin-wave theory. The resulting field-coupling phase diagram reveals that quantum fluctuations stabilize coplanar order across the entire parameter range, giving rise to a characteristic sequence of magnetization plateaux. Near the quantum-spin-liquid window $0.06\lesssim J_2/J_1\lesssim 0.16$, which extends to magnetic field $B\sim J_1$, we identify overlapping $m=1/3$ and $m=1/2$ plateaux—a distinctive hallmark of the system’s proximity to the low-field spin-liquid regime. The excellent quantitative agreement between DMRG and self-consistent one-loop spin-wave calculations demonstrates that semiclassical approaches can reliably capture and parameterize the plateau phases of triangular quantum antiferromagnets.

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• Antiferromagnetism
• Frustrated magnetism
• Spin liquid