Shiyuan Wang#, Yao Wang#, Shaohua Yan#, Cong Wang#, Bingke Xiang,Keyi Liang,Qiushi He,Kenji Watanabe,Takashi Taniguchi, Shangjie Tian, Hechang Lei, Wei Ji, Yang Qi, Yihua Wang*
Abstract
In two-dimensional (2D) ferromagnets, anisotropy is essential for the magnetic ordering as dictated by the Mermin-Wagner theorem. But when competing anisotropies are present, the phase transition becomes nontrivial. Here, utilizing highly sensitive susceptometry of scanning superconducting quantum interference device microscopy, we probe the spin correlations of ABC-stacked CrBr3 under zero magnetic field. We identify a plateau feature in susceptibility above the critical temperature (�C) in thick samples. It signifies a crossover regime induced by the competition between easy-plane intralayer exchange anisotropy versus uniaxial interlayer anisotropy. The evolution of the critical behavior from the bulk to 2D shows that the competition between the anisotropies is magnified in the reduced dimension. It leads to a strongly frustrated ferromagnetic transition in the bilayer with fluctuation on the order of �C, which is distinct from both the monolayer and the bulk. Our observation demonstrates unconventional 2D critical behavior on a honeycomb lattice.
A superatom is any cluster of atoms that collectively exhibits some properties of single atoms. When arranged into crystals through the noncovalent bonds, they can be readily assembled into nanostructures, because the reduced cohesive energy of the noncovalent bonds makes it easier to cleave the material. It is not yet clear whether such weakened energetic interaction is accompanied by a suppressed electronic interaction among the superatoms. To that end, we explore exotic electronic structures on the surface of one superatomic crystal and find strong electron-electron interactions do occur. We also find that two exotic charge orders emerge.
Recently, researchers synthesized a cubic superatom, Au6Te12Se8 (ATS), and assembled it into a 3D crystal with metallicity and superconductivity. In our experiments, we observe two charge orders on the ATS surface. One is a charge density wave that forms across repeating columns of ATS cubes. The other is a polar metallic state that arises between the columns. The polar metallic states are of particular interest, suggesting the ATS surface is an antipolar metal—a type of exotic metal where metallicity and orderly, antiparallel-oriented electric dipoles coexist. The discovery of this antipoloar metal goes one step further toward the realization of multifunctional devices, which could, in principle, perform simultaneous electrical, magnetic, and optical functions. However, we have not yet examined ATS’s ferroelectricity, which is needed for electrical control of its electrical polarization.
This ATS crystal is, to the best of our knowledge, the first antipolar metal ever found and possesses the first polar metallic state hosted in superatomic units bound by noncovalent interactions. Thus, the strong electron-electron interactions, found in the 2D superatomic layers, open a category of quantum materials that contains versatile layered nanostructures exhibiting precisely tailorable electronic structures.
Abstract
Electronic properties of superatomic crystals have not been sufficiently explored due to the versatility of their building units; moreover, their interunit couplings are even poorly understood. Here, we present a joint experiment-theory investigation of a rationally designed layered superatomic crystal of Au6Te12Se8 (ATS) cubes stacked by noncovalent intercube quasibonds. We find a sequential-emerged anisotropic triple-cube charge density wave (TCCDW) and polarized metallic states below 120 K, as revealed via scanning tunneling microscopy and spectroscopy, angle-resolved photoemission spectroscopy, transport measurement, Raman spectra, and density-functional theory. The polarized states are locked in an antiparallel configuration, which is required for maintaining the inversion symmetry of the center cube in the TCCDW. The antipolar metallic states are thus interweaved by the CDW and the polarized metallic states, and primarily ascribed to electronic effects via theoretical calculations. This work not only demonstrates a microscopic picture of the interweaved CDW and polarized charge orders in the superatomic crystal of ATS, but also sheds light on expanding the existing category of quantum materials to noncovalent solids.
Jialei Miao#, Linlu Wu#, Zheng Bian, Qinghai Zhu, Tianjiao Zhang, Xin Pan, Jiayang Hu, Wei Xu, Yeliang Wang, Yang Xu, Bin Yu, Wei Ji, Xiaowei Zhang*, Jingsi Qiao*, Paolo Samorì*, and Yuda Zhao*
Abstract
Two-dimensional (2D) materials with the atomically thin thickness have attracted great interest in the post-Moore’s Law era because of their tremendous potential to continue transistor downscaling and offered advances in device performance at the atomic limit. However, the metal–semiconductor contact is the bottleneck in field-effect transistors (FETs) integrating 2D semiconductors as channel materials. A robust and tunable doping method at the source and drain region of 2D transistors to minimize the contact resistance is highly sought after. Here we report a stable carrier doping method via the mild covalent grafting of maleimides on the surface of 2D transition metal dichalcogenides. The chemisorbed interaction contributes to the efficient carrier doping without degrading the high-performance carrier transport. Density functional theory results further illustrate that the molecular functionalization leads to the mild hybridization and the negligible impact on the conduction bands of monolayer MoS2, avoiding the random scattering from the dopants. Differently from reported molecular treatments, our strategy displays high thermal stability (above 300 °C) and it is compatible with micro/nano processing technology. The contact resistance of MoS2 FETs can be greatly reduced by ∼12 times after molecular functionalization. The Schottky barrier of 44 meV is achieved on monolayer MoS2 FETs, demonstrating efficient charge injection between metal and 2D semiconductor. The mild covalent functionalization of molecules on 2D semiconductors represents a powerful strategy to perform the carrier doping and the device optimization.
Professor Paul S. Weiss, UC Presidential Chair, Distinguished Professor of Chemistry and Biochemistry and of Materials Science and Engineering and Editor-in-Chief of ACS Nano, says he prepares a figure set before the data is even available. Doing this can help chemists map out what’s missing from your research. It also lays the work out into a sort of storyboard.
Professor Phil S Baran, Darlene Shiley Chair in Chemistry at The Scripps Research Institute and Associate Editor of Journal of the American Chemical Society (JACS) equates writing a paper to writing a children’s novel. “It starts with the illustrations,” Baran says, “it’s what we do. We work on the pictures first.” Baran goes on to explain that most people don’t have time to go through an entire research paper, so the figures should be able to tell much of the story.
Another approach is to storyboard all of your data. Professor Peter License, of University of Nottingham and Associate Editor of ACS Sustainable Chemistry & Engineering, says once you have all the figures in front of you, you can see if they prove that the research answered the initial question.
II. 中文版
加州大学校长主席，化学和生物化学以及材料科学与工程杰出教授，ACS Nano主编Paul S. Weiss教授说，他在数据可用之前就准备了一个数字集。这样做可以帮助化学家找出您的研究中缺少的内容。它还将工作布置成一种故事板。
斯克里普斯研究所Darlene Shiley化学主席兼《美国化学学会杂志》（JACS）副主编Phil S Baran教授将撰写论文等同于撰写儿童小说。“它从插图开始，”巴兰说，“这就是我们所做的。我们先处理图片。巴兰继续解释说，大多数人没有时间浏览整篇研究论文，所以这些数字应该能够讲述大部分故事。
另一种方法是对所有数据进行情节提要。诺丁汉大学（University of Nottingham）教授、ACS可持续化学与工程（ACS Sustainable Chemistry & Engineering）副主编彼得·拉克（Peter License）说，一旦你把所有的数字都摆在你面前，你就可以看看它们是否证明了这项研究回答了最初的问题。
An easy way to start planning your paper is a simple outline. It’s a method that allows you to pool all of your data and organize it. Think of it as the framework to write your paper.
Professor Brent Gunnoe, Ph.D., Commonwealth Professor of Chemistry at the University of Virginia and Associate Editor of ACS Catalysis says his outlines start even before the paper is ready to write. Outlines take time to create from initial ideas. They require revisions until you have the ideal framework to build on. These revisions also help pinpoint any experiments that still need to be performed.
Professor Joan F. Brennecke, Ph.D., Professor of Chemical Engineering at the University of Texas at Austin, and Editor-in-Chief of Journal of Chemical & Engineering Data says outlines are mandatory. They need to be fully detailed and organized in a hierarchy. This level of detail makes writing the paper a simple task of filling in the sentences to link the points.
Professor Prashant Kamat, Ph.D., John A. Zahm Professor of Science at the Unviersity of Notre Dame and Editor-in-Chief of ACS Energy Letters likens the outline to a blueprint. You can’t build a house without one. You need to bring the data together to see how and where everything fits, and if you need more data.
Start outlining early, with as much detail as possible. This will help you see where and if you need to perform more experiments.
