2$k_F$ instability and chiral spin density wave at the 1/9 magnetization plateau in the kagome antiferromagnets

TL;DR

This paper investigates the complex magnetic state at the 1/9 magnetization plateau in kagome antiferromagnets, revealing a gapless chiral spin density wave driven by 2$k_F$ instability using advanced machine learning techniques.

Contribution

The study introduces a novel machine learning approach combining variational Monte Carlo, neural network quantum states, and flux insertion to analyze the plateau state.

Findings

Ground state is a gapless 1x1 chiral spin density wave.

The state results from 2$k_F$ instability of a composite Fermi liquid.

Spin chirality indicates nontrivial topological order.

Abstract

Kagome lattice antiferromagnets exhibit plethora of intriguing phases of matter. Particularly interesting state appears at the magnetic field-induced $1/9$ magnetization plateau observed in several recent experimental studies. The nature and exotic physical properties of the plateau however remain controversial due to an exceptional complexity of the state generated by geometrical frustration. Among candidate states recent studies found a $Z_3$ quantum spin liquid state, a valence bond crystal exhibiting an hourglass pattern and a valence bond crystal state with a $3\times 3$ periodicity and a windmill-shaped motif. Recent torque magnetometry measurements on YCOB single-crystal samples however indicate presence of Dirac-like spinons at $1/9$ magnetization plateau. We study properties of the plateau state using novel machine learning technique that combines variational Monte Carlo, symmetry enhanced neural network quantum states and flux insertion method. Our machine learning study reveals that the ground state at the $1/9$ plateau is a gapless $1\times 1$ chiral spin density wave caused by 2$k_F$ instability of the underlying composite Fermi liquid. The spin wave chirality results from the correlated spin order that reflects its nontrivial topology.