Yanyan Geng (耿燕燕)†, Manyu Wang (王曼雨)†, Shumin Meng (孟淑敏), Shuo Mi (米烁), Chang Li (李畅), Huiji Hu (胡会吉), Jianfeng Guo (郭剑锋), Rui Xu (许瑞), Fei Pang (庞斐), Wei Ji (季威), Weichang Zhou (周伟昌)* and Zhihai Cheng (程志海)*
Abstract:
Transition-metal dichalcogenides hosting multiple competing structural and electronic phases are thus ideal platforms for constructing polytype heterostructures with emergent quantum properties. However, controlling phase transitions to form diverse heterostructures inside a single crystal remains challenging. In this study, we realize vertical/lateral polytype heterostructures in a hole-doped Mott insulator via thermal annealing-induced structural transitions. Raman spectroscopy, atomic force microscopy and scanning Kelvin probe force microscopy confirm the coexistence of T-H polytype heterostructures. Atomic-scale scanning tunneling microscopy / spectroscopy measurements reveal the transparent effect in 1H/1T vertical heterostructures, where positive bias v oltage induces in a pronounced superposition of the sqrt13 × sqrt13 CDW of the 1T-layer on the 1H-layer. By systematically comparing the 1T/1H and 1T/1T interfaces, we demonstrate that the metallic 1H-layer induces a Coulomb screening effect on the 1T-layer, suppressing the formation of CDW domain walls and forming more ordered electronic states. These results clarify the interfacial coupling between distinct quantum many-body phases and establish a controllable pathway for constructing two-dimensional polytype heterostructures with tunable electronic properties.
Li Huang, Yuqing Xing, Qi Zheng, Senhao Lv, Lan Chen, Hui Chen, Haitao Yang, Wei Ji and Hong-Jun Gao*
Abstract:
Altermagnetic materials, with real-space antiferromagnetic arrangement and reciprocal-space anisotropic spin splitting, have attracted much attention. However, the spin splitting is small in most altermagnetic materials, which is a disadvantage to their application in electronic devices. In this study, based on symmetry analysis and the first-principles electronic structure calculations, we predict for the first time two Luttinger compensated bipolarized magnetic semiconductors Mn(CN)2 and Co(CN)2 with isotropic spin splitting as in the ferromagnetic materials. Our further analysis shows that the Luttinger compensated magnetism here depends not only on spin group symmetry, but also on the crystal field splitting and the number of d-orbital electrons. In addition, the polarized charge density indicates that both Mn(CN)2 and Co(CN)2 have the quasi-symmetry T{tau} , resulting from the crystal field splitting and the number of d-orbital electrons. The Luttinger compensated magnetism not only has the zero total magnetic moment as the antiferromagnetism, but also has the isotropic spin splitting as the ferromagnetism, thus our work not only provides theoretical guidance for searching Luttinger compensated magnetic materials with distinctive properties, but also provides a material basis for the application in spintronic devices.
Altermagnetic materials, with real-space antiferromagnetic arrangement and reciprocal-space anisotropic spin splitting, have attracted much attention. However, the spin splitting is small in most altermagnetic materials, which is a disadvantage to their application in electronic devices. In this study, based on symmetry analysis and the first-principles electronic structure calculations, we predict for the first time two Luttinger compensated bipolarized magnetic semiconductors Mn(CN)2 and Co(CN)2 with isotropic spin splitting as in the ferromagnetic materials. Our further analysis shows that the Luttinger compensated magnetism here depends not only on spin group symmetry, but also on the crystal field splitting and the number of d-orbital electrons. In addition, the polarized charge density indicates that both Mn(CN)2 and Co(CN)2 have the quasi-symmetry T{\tau} , resulting from the crystal field splitting and the number of d-orbital electrons. The Luttinger compensated magnetism not only has the zero total magnetic moment as the antiferromagnetism, but also has the isotropic spin splitting as the ferromagnetism, thus our work not only provides theoretical guidance for searching Luttinger compensated magnetic materials with distinctive properties, but also provides a material basis for the application in spintronic devices.
Two‑dimensional multiferroics promise low‑power, multifunctional devices, yet the intrinsic coexistence and mutual control of three coupled ferroic orders in a single layer remains elusive. Here, we identify pentagonal monolayer FeO2 as an intrinsic triferroic altermagnet where ferroelectric (FE), ferroelastic (FA), and altermagnetic (AM) orders coexist and tightly coupled, accompanied by a competing antiferroelectric (AFE) phase using first‑principles calculations. The solely presence of glide mirror Mx symmetry in a FeO2 sublayer, with the breaking of four‑fold rotation C4z symmetry, induces in‑plane vector ferroelectricity and twin‑related ferroelastic strains. Both FE and AFE phases break combined parity–time symmetry and display sizable altermagnetic spin splitting with Néel temperatures over 200 K. Electric‑field induced rotation of the FE polarization reverses the sign of the spin splitting, while in‑plane uniaxial strain triggers ferroelastic switching that simultaneously rotates the FE polarization vector by 90° and reverses the AM state. These electric‑field‑ and strain‑mediated pathways interlink six distinct polarization states that can be selected purely by electric fields and/or mechanical strain. This work extends intrinsic triferroicity to pentagonal monolayers and outlines a symmetry‑based route toward mechanically and electrically configurable altermagnetic spintronics.
Two-dimensional (2D) moire superlattices have emerged as a versatile platform for uncovering exotic quantum phases, many of which arise in bilayer systems exhibiting Archimedean tessellation patterns such as triangular, hexagonal, and kagome lattices. Here, we propose a strategy to engineer semiregular tessellation patterns in untwisted bilayer graphene by applying anisotropic epitaxial tensile strain (AETS) along crystallographic directions. Through force-field and first principles calculations, we demonstrate that AETS can induce a rich variety of semiregular tessellation geometries, includ ing truncated hextille, prismatic pentagon, and brick-phase arrangements. Characteristic electronic Dirac and flat bands of the lattice models associated with these semiregular tessellations are observed near the Fermi level, arising from interlayer interactions generated by the spatial rearrangement of AB, BA, and SP domains. Furthermore, the real-space observations of electronic kagome, distorted Lieb, brick-like, and one-dimensional stripe lattices demonstrate that AETS enables tunable semiregular tessellation lattices. Our study identifies AETS as a promising new degree of freedom in moir´e engineering, offering a reproducible and scalable platform for exploring exotic electronic lattices in moire systems.
