Semiclassical analysis of a magnetization plateau in a 2D frustrated ferrimagnet

TL;DR

This paper investigates a 1/3 magnetization plateau in a frustrated 2D ferrimagnet using semiclassical methods, revealing quantum effects that broaden the plateau and discovering an exotic chiral liquid phase near its destabilization.

Contribution

It introduces a semiclassical large-S expansion to analyze the magnetization plateau and identifies a novel chiral liquid phase in a frustrated kagome lattice model.

Findings

Quantum fluctuations broaden the classical magnetization plateau.

A chiral liquid phase emerges near the plateau destabilization.

The model's relevance to the volborthite material is discussed.

Abstract

We use a semiclassical large-$S$ expansion to study a plateau at $1/3$ saturation in the magnetization curve of a frustrated ferrimagnet on a spatially anisotropic kagom\'{e} lattice. The spins have both ferromagnetic and antiferromagnetic nearest-neighbor Heisenberg couplings, and a frustrating next-nearest-neighbor coupling in one lattice direction. The magnetization plateau appears at the classical level for a certain range of couplings, and quantum fluctuations significantly broaden it at both ends. Near the region of the phase diagram where the classical plateau destabilizes, we find an exotic "chiral liquid" phase that preserves translational and $U(1)$ spin symmetry, in which bound pairs of magnons with opposite spins are condensed. We show how this state is obtained naturally from a relativistic field theory formulation. We comment on the relevance of the model to the material $\text{Cu}_3\text{V}_2\text{O}_7\text{(OH)}_2 \cdot 2\text{H}_2\text{O}$ (volborthite).