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

Hiroaki Hayashi; Han Li; Feng-Feng Song; Xu-Guang Zhou; Akira Matsuo; Taeyun Kim; Enze Lv; Yuto Ishii; Zhe Qu; Gang Su; Koichi Kindo; Kwang-Yong Choi; Wei Li; Yasuhiro H. Matsuda

arXiv · 2605.17995

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

Hiroaki Hayashi·Han Li·Feng-Feng Song·Xu-Guang Zhou·Akira Matsuo·Taeyun Kim·Enze Lv·Yuto Ishii·Zhe Qu·Gang Su·Koichi Kindo·Kwang-Yong Choi·Wei Li·Yasuhiro H. Matsuda

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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.

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Hiroaki Hayashi, Han Li, Feng-Feng Song, Xu-Guang Zhou, Akira Matsuo, Taeyun Kim, Enze Lv, Yuto Ishii, Zhe Qu, Gang Su, Koichi Kindo, Kwang-Yong Choi, Wei Li, Yasuhiro H. Matsuda. 2026-05-18. $5/9-$Magnetization Plateau and Spin Supersolidity in YCu$_3$(OD)$_{7-x}$Br$_{2+x}$ under Magnetic Fields up to 120~T. https://arxiv.org/abs/2605.17995

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