Han Myung-Geun, Garlow Joseph A, Liu Yu, Zhang Huiqin, Li Jun, DiMarzio Donald, Knight Mark W, Petrovic Cedomir, Jariwala Deep, Zhu Yimei
Condensed Matter Physics and Materials Science , Brookhaven National Laboratory , Upton , New York 11973 , United States.
Department of Materials Science and Chemical Engineering , Stony Brook University , Stony Brook , New York 11794 , United States.
Nano Lett. 2019 Nov 13;19(11):7859-7865. doi: 10.1021/acs.nanolett.9b02849. Epub 2019 Nov 4.
Two-dimensional (2D) van der Waals (vdW) materials show a range of profound physical properties that can be tailored through their incorporation in heterostructures and manipulated with external forces. The recent discovery of long-range ferromagnetic order down to atomic layers provides an additional degree of freedom in engineering 2D materials and their heterostructure devices for spintronics, valleytronics, and magnetic tunnel junction switches. Here, using direct imaging by cryo-Lorentz transmission electron microscopy we show that topologically nontrivial magnetic-spin states, skyrmionic bubbles, can be realized in exfoliated insulating 2D vdW CrGeTe. Due to the competition between dipolar interactions and uniaxial magnetic anisotropy, hexagonally packed nanoscale bubble lattices emerge by field cooling with magnetic field applied along the out-of-plane direction. Despite a range of topological spin textures in stripe domains arising due to pair formation and annihilation of Bloch lines, bubble lattices with single chirality are prevalent. Our observation of topologically nontrivial homochiral skyrmionic bubbles in exfoliated vdW materials provides a new avenue for novel quantum states in atomically thin insulators for magneto-electronic and quantum devices.
二维（2D）范德华（vdW）材料展现出一系列深刻的物理特性，这些特性可通过将其纳入异质结构并借助外力进行调控。近期关于直至原子层的长程铁磁序的发现，为二维材料及其用于自旋电子学、谷电子学和磁隧道结开关的异质结构器件的工程设计提供了额外的自由度。在此，我们利用低温洛伦兹透射电子显微镜进行直接成像，结果表明在剥离的绝缘二维范德华CrGeTe中可实现拓扑非平凡磁自旋态——斯格明子泡。由于偶极相互作用与单轴磁各向异性之间的竞争，通过沿面外方向施加磁场进行场冷时会出现六边形排列的纳米级泡状晶格。尽管由于布洛赫线的成对形成和湮灭，条纹域中存在一系列拓扑自旋纹理，但具有单一手性的泡状晶格更为普遍。我们在剥离的范德华材料中对拓扑非平凡同手性斯格明子泡的观测，为用于磁电子和量子器件的原子级薄绝缘体中的新型量子态开辟了一条新途径。
