Wong Ping Kwan Johnny, Zhang Wen, Bussolotti Fabio, Yin Xinmao, Herng Tun Seng, Zhang Lei, Huang Yu Li, Vinai Giovanni, Krishnamurthi Sridevi, Bukhvalov Danil W, Zheng Yu Jie, Chua Rebekah, N'Diaye Alpha T, Morton Simon A, Yang Chao-Yao, Ou Yang Kui-Hon, Torelli Piero, Chen Wei, Goh Kuan Eng Johnson, Ding Jun, Lin Minn-Tsong, Brocks Geert, de Jong Michel P, Castro Neto Antonio H, Wee Andrew Thye Shen
Centre for Advanced 2D Materials (CA2DM) and Graphene Research Centre (GRC), National University of Singapore, 6 Science Drive 2, Singapore, 117546, Singapore.
Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore, 117542, Singapore.
Adv Mater. 2019 Jun;31(23):e1901185. doi: 10.1002/adma.201901185. Epub 2019 Apr 18.
Monolayer VSe , featuring both charge density wave and magnetism phenomena, represents a unique van der Waals magnet in the family of metallic 2D transition-metal dichalcogenides (2D-TMDs). Herein, by means of in situ microscopy and spectroscopic techniques, including scanning tunneling microscopy/spectroscopy, synchrotron X-ray and angle-resolved photoemission, and X-ray absorption, direct spectroscopic signatures are established, that identify the metallic 1T-phase and vanadium 3d electronic configuration in monolayer VSe grown on graphite by molecular-beam epitaxy. Element-specific X-ray magnetic circular dichroism, complemented with magnetic susceptibility measurements, further reveals monolayer VSe as a frustrated magnet, with its spins exhibiting subtle correlations, albeit in the absence of a long-range magnetic order down to 2 K and up to a 7 T magnetic field. This observation is attributed to the relative stability of the ferromagnetic and antiferromagnetic ground states, arising from its atomic-scale structural features, such as rotational disorders and edges. The results of this study extend the current understanding of metallic 2D-TMDs in the search for exotic low-dimensional quantum phenomena, and stimulate further theoretical and experimental studies on van der Waals monolayer magnets.
单层VSe₂兼具电荷密度波和磁性现象，是金属二维过渡金属二硫属化物（2D-TMDs）家族中一种独特的范德华磁体。在此，通过原位显微镜和光谱技术，包括扫描隧道显微镜/光谱、同步辐射X射线和角分辨光电子能谱以及X射线吸收，建立了直接光谱特征，确定了通过分子束外延生长在石墨上的单层VSe₂中的金属1T相和钒3d电子构型。元素特异性X射线磁圆二色性结合磁化率测量，进一步揭示单层VSe₂是一种受挫磁体，其自旋表现出微妙的相关性，尽管在低至2 K和高达7 T磁场下不存在长程磁序。这一观察结果归因于铁磁和反铁磁基态的相对稳定性，这是由其原子尺度的结构特征，如旋转无序和边缘所导致的。这项研究的结果扩展了目前对金属2D-TMDs在寻找奇异低维量子现象方面的理解，并激发了对范德华单层磁体的进一步理论和实验研究。
