$J_1-J_2$ Triangular Lattice Antiferromagnet in a Magnetic Field

TL;DR

This study combines DMRG simulations and spin-wave theory to map the phase diagram of the $J_1-J_2$ triangular-lattice antiferromagnet in a magnetic field, revealing stable coplanar order and multiple magnetization plateaux.

Contribution

It provides a comprehensive analysis showing that semiclassical spin-wave methods accurately describe quantum plateau phases near a spin-liquid regime.

Findings

Quantum fluctuations stabilize coplanar order.

Identification of overlapping 1/3 and 1/2 magnetization plateaux.

Good agreement between DMRG and spin-wave calculations.

Abstract

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 $0.06 \lesssim J_2/J_1 \lesssim 0.14$, 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.