Quantum stabilization of classically unstable plateau structures

TL;DR

This paper introduces a semiclassical method to estimate zero-point energies of collinear spin configurations in frustrated quantum antiferromagnets, explaining the stabilization of certain magnetization plateaus beyond classical predictions.

Contribution

It develops a novel semiclassical approach to analyze the stability of collinear states in quantum antiferromagnets, even when these states are not classically stable.

Findings

Stabilization of a 1/2 magnetization plateau in the frustrated square-lattice antiferromagnet.

Prediction of a stable 1/3 plateau in the anisotropic triangular antiferromagnet.

Agreement of the method's predictions with exact diagonalization and experimental results.

Abstract

Motivated by the intriguing report, in some frustrated quantum antiferromagnets, of magnetization plateaus whose simple collinear structure is {\it not} stabilized by an external magnetic field in the classical limit, we develop a semiclassical method to estimate the zero-point energy of collinear configurations even when they do not correspond to a local minimum of the classical energy. For the spin-1/2 frustrated square-lattice antiferromagnet, this approach leads to the stabilization of a large 1/2 plateau with "up-up-up-down" structure for J_2/J_1>1/2, in agreement with exact diagonalization results, while for the spin-1/2 anisotropic triangular antiferromagnet, it predicts that the 1/3 plateau with "up-up-down" structure is stable far from the isotropic point, in agreement with the properties of Cs_2CuBr_4.