Observation of a magnetic phase transition in monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>NiP</mml:mi><mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>
Lili Hu, Hao-Xin Wang, Yuzhong Chen, Kang Xu, Ming-Rui Li, Haiyun Liu, Peng Gu, Yubin Wang, Mengdi Zhang, Hong Yao, Qihua Xiong
Abstract
Monolayer magnet of $\mathit{XY}$ type composes a pivotal part of the two-dimensional magnetism. As an important suspected $\mathit{XY}$-type antiferromagnet, whether $1L \mathrm{NiP}{\mathrm{S}}_{3}$ exhibits magnetic order remains elusive. Herein by helicity-resolved Raman and ultrafast spectroscopy of $\mathrm{NiP}{\mathrm{S}}_{3}$ from bulk to monolayer, we find that $1L \mathrm{NiP}{\mathrm{S}}_{3}$ is magnetically ordered with a Berezinskii-Kosterlitz-Thouless (BKT) transition at ${T}_{\mathrm{BKT}}\ensuremath{\approx}140$ K. We have also performed large-scale density-matrix renormalization-group calculations to verify the ground state zigzag antiferromagnetic order and Monte Carlo simulation to confirm the BKT-transition temperature in $1L \mathrm{NiP}{\mathrm{S}}_{3}$. Our investigations establish $1L \mathrm{NiP}{\mathrm{S}}_{3}$ to be an $\mathit{XY}$ antiferromagnet with a relatively high-temperature BKT transition, providing an important platform for investigating complex couplings and topological excitations.