Renhong Wang (王人宏), Cong Wang (王聪)*, Ruixuan Li (李睿宣), Deping Guo (郭的坪), Jiaqi Dai (戴佳琦), Canbo Zong (宗灿波), Weihan Zhang (张伟 涵), and Wei Ji (季威)*
Abstract:
Kagome materials are known for hosting exotic quantum states, including quantum spin liquids, charge density waves, and unconventional superconductivity. The search for kagome monolayers is driven by their ability to exhibit neat and well-defined kagome bands near the Fermi level, which are more easily realized in the absence of interlayer interactions. However, this absence also destabilizes the monolayer forms of many bulk kagome materials, posing significant challenges to their discovery. In this work, we propose a strategy to address this challenge by utilizing oxygen vacancies in transition metal oxides within a “1+3” design framework. Through high-throughput computational screening of 349 candidate materials, we identified 12 thermodynamically stable kagome monolayers with diverse electronic and magnetic properties. These materials were classified into three categories based on their lattice geometry, symmetry, band gaps, and magnetic configurations. Detailed analysis of three representative monolayers revealed kagome band features near their Fermi levels, with orbital contributions varying between oxygen 2p and transition metal d states. This study demonstrates the feasibility of the “1+3” strategy, offering a promising approach to uncovering low-dimensional kagome materials and advancing the exploration of their quantum phenomena.
Xiangqi Wang†, Cong Wang†, Yupeng Wang†, Chunhui Ye, Azizur Rahman, Min Zhang, Suhan Son, Jun Tan*, Zengming Zhang*, Wei Ji*, Je-Geun Park6,7,8, and Kai-Xuan Zhang†*
Abstract:
Van der Waals (vdW) magnets, with their two-dimensional (2D) atomic structures, provide a unique platform for exploring magnetism at the nanoscale. Although there have been numerous reports on their diverse quantum properties, the emergent interfacial magnetism— artificially created at the interface between two layered magnets—remains largely unexplored. This work presents observations of such emergent interfacial magnetism at the ferromagnet/antiferromagnet interface in a vdW heterostructure. We report the discovery of an intermediate Hall resistance plateau in the anomalous Hall loop, indicative of emergent interfacial antiferromagnetism fostered by the heterointerface. This plateau can be stabilized and further manipulated under varying pressures but collapses under high pressures over 10 GPa. Our theoretical calculations reveal that charge transfer at the interface is pivotal in establishing the interlayer antiferromagnetic spin-exchange interaction. This work illuminates the previously unexplored emergent interfacial magnetism at a vdW interface comprised of a ferromagnetic metal and an antiferromagnetic insulator, and highlights its gradual evolution under increasing pressure. These findings enrich the portfolio of emergent interfacial magnetism and pave the way for future investigations on vdW magnetic interfaces and the development of next-generation spintronic devices.
Yanyan Geng+, Haoyu Dong+, Renhong Wang+, Jianfeng Guo, Shuo Mi, Le Lei, Yan Li, Li Huang, Fei Pang, Rui Xu, Weiqiang Yu, Hong-Jun Gao, Wei Ji*, Weichang Zhou*, and Zhihai Cheng*
Abstract:
The delicate interplay among the complex intra-/inter-layer electron-electron and electron-lattice interactions is the fundamental prerequisite of these exotic quantum states, such as superconductivity, nematic order, and checkerboard charge order. Here we explore the filling-dependent multiple stable intertwined electronic and atomic orders of flat-band state of 1T-TaS2 encompassing hole order, phase orders, coexisting left- and right-chiral orders and mixed phase/chiral orders via scanning tunneling microscopy (STM). Combining first principles calculations, the novel emergent electronic/ atomic orders can be attributed to the weakening of electron-electron correlations and stacking-dependent interlayer interactions. Moreover, achiral intermediate ring-like clusters and nematic charge density wave (CDW) states are successfully realized in intralayer chiral domain wall and interlayer heterochiral stacking regions through chiral overlap configurations. Our study not only deepens the understanding of filling-dependent electronic/atomic orders in flat-band systems, but also offers new perspectives for exploring exotic quantum states in correlated electronic systems.
Zhongqin Zhang† , Jiaqi Dai† , Cong Wang , Hua Zhu , Fei Pang , Zhihai Cheng, and Wei Ji*
Abstract:
In recent years, kagome materials have attracted significant attention due to their rich emergent phenomena arising from the quantum interplay of geometry, topology, spin, and correlations. However, in the search for kagome materials, it has been found that bulk compounds with electronic properties related to the kagome lattice are relatively scarce, primarily due to the hybridization of kagome layers with adjacent layers. Therefore, researchers have shown increasing interest in the discovery and construction of two-dimensional (2D) kagome materials, aiming to achieve clean kagome bands near the Fermi level in monolayer or few-layer systems. Substantial advancements have already been made in this area. In this review, we summarize the current progress in the construction and development of 2D kagome materials. We begin by introducing the geometric and electronic structures of the kagome lattice model and its variants, followed by discussions on the experimental realizations and electronic structure characterizations of 2D kagome materials. Finally, we provide an outlook on the future developments of 2D kagome materials.
Two-dimensional Janus materials exhibit unique physical properties due to broken inversional symmetries. However, it remains elusive to synthesize Janus monolayer crystals with tailored long-range magnetic orders. Here, we show a 2 ×√𝟑 charge density wave (CDW) transition and regulations of magnetization in a uniform Janus CrTeSe monolayer, selectively selenized from a pristine CrTe2 monolayer using molecular beam epitaxy. Scanning transmission electron microscopy images indicate the high quality and uniformity of the Janus structure. Spin-polarized scanning tunneling microscopy/spectroscopy measurements and density functional theory calculations unveil a robust zigzag antiferromagnetic order and the CDW transition in the CrTeSe monolayer. The one-side selenization breaks the vertical inversion symmetry, rotating the magnetic moment directions to the in-plane direction. The CDW transition opens a gap at the Fermi level and reorients the magnetic moments in tilted directions. Our work demonstrates the construction of large-area Janus structures and the tailoring of electronic and magnetic properties of two-dimensional Janus layers.
