Yangjin Lee#, Linxuan Li#, Weihan Zhang#, Uje Choi, Kihyun Lee, Young-Min Kim, Wei Ji*, Wu Zhou*, Kwanpyo Kim*, and Alex Zettl*
Abstract:
Low-dimensional magnetic materials have garnered significant interest due to their unique physical properties and potential applications. Nevertheless, the synthesis of one-dimensional (1D) magnetic materials presents challenges, and the properties of these 1D materials at the single-chain limit have not been well investigated. We here explore experimentally and theoretically 1D CrX2 (X= Cl, Br, I) magnetic single-chains residing within carbon nanotubes. Single chains of CrX2 are confirmed by atomic-resolution scanning transmission electron microscopy imaging and spectroscopy analysis. Electron energy loss spectroscopy clearly reveals the high-spin state of Cr atoms within the chain. Notably, we present the first precise measurement and analysis of Cr spin state at the single-chain level, revealing that these spin states can be controlled by the local atomic bonding configuration (CrX2 versus CrX3 phases). Density functional theory calculations support the structural stability and provide the magnetic and electronic properties of the 1D CrX2 chains.
Zeyu Liu, Xianghua Kong, Zewen Wu, Linwei Zhou, Jingsi Qiao and Wei Ji
Abstract:
Moire superlattices in twisted homo-bilayers have revealed exotic electronic states, including unconventional superconductivity and correlated insulating phases. However, their fabrication process often introduces moire disorders, hindering reproducibility and experimental control. Here, we propose an alternative approach using gradient strain to construct moire superlattices in untwisted bilayer graphene (gs-BLG). Through force-field and first-principles calculations, we show that gs-BLG exhibits kagome-like interlayer spacing distributions and strain-tunable kagome electronic bands. The competition between interlayer coupling and in-plane strain relaxation leads to distinct structural deformations, giving rise to three forms of diatomic kagome lattices: subtle, pronounced, and distorted. kagome electronic bands are identified near the Fermi level in their band structures. Modulating strain gradients enables tailoring bandwidths and signs of hopping parameters of these kagome bands, providing a versatile platform for studying exotic electronic phases. Our findings establish gradient strain as an alternative to twist engineering, opening an avenue for exploring emergent electronic phases in graphene-based systems.
As a fundamental structural feature, the symmetry of materials determines the exotic quantum properties in transition metal dichalcogenides (TMDs) with charge density waves (CDWs). The Janus structure, an artificially constructed lattice, provides an opportunity to tune the electronic structures and their associated behavior, such as CDW states. However, limited by the difficulties in atomic-level fabrication and material stability, the experimental visualization of the CDW states in two-dimensional (2D) TMDs with Janus structure is still rare. Here, using surface selenization of VTe2, we fabricated monolayer Janus VTeSe. With scanning tunneling microscopy, we observed and characterized an unusual sqrt13 x sqrt13 CDW state with threefold rotational symmetry breaking. Combined with theoretical calculations, we find that this CDW state can be attributed to the magnetic-involved charge modulation in the Janus VTeSe, rather than the conventional electron-phonon coupling. Our findings provide a promising platform for studying the CDW states and artificially tuning the electronic properties of the 2D TMDs toward the related fundamental and applied studies.
Two-dimensional (2D) non-van der Waals (vdW) Cr5Te8 has attracted widespread research interest for its air stability and thickness-dependent magnetic properties. However, the growth of large-scale ultrathin 2D Cr5Te8 remains challenging. Here, we selected GaTe powder as the precursor to supply Te monomers and fabricated submillimeter 2D Cr5Te8 nanosheets. By optimizing the growth temperature and source–substrate distance (DSS), we successfully achieved Cr5Te8 nanosheets with a lateral size of up to ∼0.19 mm and corresponding thickness down to ∼4.8 nm. The role of GaTe is to enhance the efficient Te atom concentration, which promotes the lateral growth of Cr5Te8 nanosheets. Furthermore, our findings reveal the appearance of Cr5Te8 nanosheets exhibiting serrated edges and a stacked structure like those of wedding cakes. Magnetic property measurement revealed the intense out-of-plane ferromagnetism in Cr5Te8, with a Curie temperature (TC) of 172 K. This work paves the way for the controllable growth of submillimeter ultrathin 2D ferromagnetic crystals and lays the foundation for the future synthesis of millimeter ultrathin ferromagnets.
Yating Li, Mengmeng Niu, Junpeng Zeng, Quan Zhou, Xu Wu, Wei Ji, Yeliang Wang, Ren Zhu, Jingsi Qiao, Jianbin Xu, Yi Shi, Xinran Wang, and Daowei He
Abstract:
Organic semiconductors are highly promising as channel materials for energy-efficient, cost-effective, and flexible electronics. However, grain boundaries (GBs) can cause significant device performance variation, posing a major challenge for the development of high-performance organic circuits. In this work, we effectively passivated GB-induced traps in monolayer organic thin-film transistors (OTFTs) via p-type doping with the organic salt TrTPFB. The doping strategy broadens the mobility edge, effectively shielding GB-induced energy barriers and Coulomb scattering, and promotes deeper nonlocalized hybridization states for conduction. Consequently, the charge transport mechanism transitions from multiple trapping and release (MTR) to a more band-like behavior, even when GBs are present within the device channel. The doped OTFTs demonstrate ultralow mobility variation (1.4%) and threshold voltage variation (4.9%), as well as record-low contact resistant of RC = 0.6 Ω·cm, outperforming most single-crystal technologies. These performance metrics render doped monolayer polycrystalline films highly promising candidates for industrial-scale organic electronics.
