$5/9-$Magnetization Plateau and Spin Supersolidity in YCu$_3$(OD)$_{7-x}$Br$_{2+x}$ under Magnetic Fields up to 120~T

TL;DR

This study reveals a 5/9 magnetization plateau and potential spin supersolidity in YCu₃(OD)₇−ₓBr₂+ₓ under high magnetic fields, combining experimental measurements and tensor-network modeling to understand the magnetic phases.

Contribution

The paper introduces the first observation of the 5/9 magnetization plateau in YCu₃(OD)₇−ₓBr₂+ₓ and models its origin using anisotropic Heisenberg Hamiltonians with tensor-network calculations.

Findings

Identification of a 5/9 fractional magnetization plateau.

Quantitative modeling of magnetization curves with tensor-network calculations.

Theoretical prediction of a spin supersolid phase between 1/3 and 5/9 plateaus.

Abstract

We performed high-precision magnetization measurements up to 120~T on three compositions of the newly discovered kagome antiferromagnet YCu$_3$(OD)$_{7-x}$Br$_{2+x}$ (YCOB), revealing a previously unobserved 5/9 fractional magnetization plateau. All YCOB samples with different Br$^-$ concentrations exhibit nearly identical magnetization curves below 60~T, whereas the 5/9 plateau appears at markedly different fields in the ultrahigh-field regime. By modeling the experimental data using tensor-network calculations, we derive the effective spin Hamiltonians for the YCOB family with three spatially anisotropic Heisenberg couplings (the 3$J$-type model), which quantitatively reproduces the measured magnetization processes and captures the composition-dependent evolution of the 5/9 plateau. Furthermore, our theoretical analysis suggests the emergence of a spin supersolid phase in the field window between the 1/3 and 5/9 plateaus, which is sensitive to spin exchange parameters and accounts for the significant variation in the critical fields of the 5/9 plateau observed among different YCOB compositions.