Efficient energy transfer in a hybrid organic-inorganic van der Waals heterostructure

Efficient energy transfer in a hybrid organic-inorganic van der Waals heterostructure

Xiaoqing Chen#, Huijuan Zhao#, Ruixiang Fei, Chun Huang, Jingsi Qiao, Cheng Sun, Haiming Zhu, Li Zhan, Zehua Hu, Songlin Li, Li Yang, Zemin Tang, Lianhui Wang, Yi Shi, Wei Ji, Jian-Bin Xu, Li Gao*, Xuetao Gan* & Xinran Wang*

Two-dimensional (2D) materials offer strong light-matter interaction and design flexibility beyond bulk semiconductors, but an intrinsic limit is the low absorption imposed by the atomic thickness. A long-sought-after goal is to achieve complementary absorption enhancement through energy transfer (ET) to break this limit. However, it is found challenging due to the competing charge transfer (CT) process and lack of resonance in exciton states. Here, we report highly efficient ET in a 2D hybrid organic-inorganic heterostructure (HOIST) of Me-PTCDI/WS2. Resonant ET is observed leading to enhanced WS2 photoluminescence (PL) by 124 times. We identify Dexter exchange between the Frenkel state in donor and an excited 2s state in acceptor as the main ET mechanism, as supported by density functional theory calculations. We further demonstrate ET-enhanced phototransistor devices with enhanced responsivity by nearly 1000 times without sacrificing the response time. Our results expand the understanding of interlayer relaxation processes in 2D materials and open opportunities in optoelectronic devices.

Robust Mottness and tunable interlayer magnetism in Nb3X8 (X = F, Cl, Br, I) bilayers

Robust Mottness and tunable interlayer magnetism in Nb3X8 (X = F, Cl, Br, I) bilayers

Zhongqin Zhang, Jiaqi Dai, Cong Wang*, Zhihai Cheng, and Wei Ji*

Kagome materials have attracted extensive attention due to their correlated properties. The breathing kagome material system Nb3F8, Nb3Cl8, Nb3Br8, Nb3I8 is regarded as a Mott insulator. However, studies on the influence of interlayer coupling on its magnetic and Mott properties are lacking. In this work, we investigated the effect of interlayer coupling on bilayer properties of each Nb3X8 (X = F, Cl, Br, I) compound via density functional theory (DFT) calculations, considering 24 stacking configurations per material. We found that each bilayer material is a Mott insulator. Due to the competition between interlayer Pauli repulsion and hopping, most interlayer magnetism is AFM, a small number of cases show AFM-FM degeneracy, and the magnetic ground state of 3 configurations is interlayer FM, i.e., tunable interlayer magnetism occurs. This robustness of Mott states coexisting with tunable interlayer magnetism provide novel and comprehensive analysis and insights for the research of breathing kagome Mott insulators.

Anisotropic Etching Patterns in 2D Cr5Te8 Nanosheets and Their Arduous Saturation Magnetization

Anisotropic Etching Patterns in 2D Cr5Te8 Nanosheets and Their Arduous Saturation Magnetization

Hanxiang Wu, Zuoquan Tan, Zhaxi Suonan, Shanshan Chen, Rui Xu, Wei Ji, Zhihai Cheng, and Fei Pang*

Although 2D self-intercalated Cr5Te8 has been successfully synthesized via chemical vapor deposition (CVD), its etching behavior remains largely unexplored. Etching, as the inverse process of material growth, is essential for understanding growth mechanisms and fabricating nanosheet patterns. Herein, we explore the anisotropic etching of 2D Cr5Te8 assisted by an excess Te supply. The etching process initiates from both the surface and the edge, creating distinct holes and nanoribbons with triangular or hexagonal shapes. To the best of our knowledge, this is the first report on controllable anisotropic etching patterns in 2D Cr5Te8. Furthermore, magnetic measurements reveal ferromagnetism in the etched nanosheets with a Curie temperature (TC) of 164 K, slightly lower than that of the unetched nanosheets. The etched nanosheets exhibit an enhanced saturated magnetic field of 38.5 kOe, approximately 3.2 times that of the unetched nanosheets. This enhancement in the saturated magnetic field is attributed to the pattern-induced strengthening of the reentrant stray field. This study offers a new direction for preparing patterned 2D materials and opens a novel avenue for modulating 2D magnetism.

Tunable altermagnetism via interchain engineering in parallel-assembled atomic chains

Tunable altermagnetism via interchain engineering in parallel-assembled atomic chains

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Deping Guo, Canbo Zong, Weihan Zhang, Cong Wang*, Junwei Liu*, and Wei Ji*

Altermagnetism has recently drawn considerable attention in three- and two-dimensional materials. Here we extend this concept to quasi-one-dimensional (Q1D) monolayers assembled from single-atomic magnetic chains. Through systematically examining nine types of structures, two stacking orders, intra- and interchain magnetic couplings, we identify four out of 30 promising structural prototypes for hosting altermagnetism, which yields 192 potential monolayer materials. We further confirm eight thermodynamically stable Q1D monolayers via high-throughput calculations. Using symmetry analysis and first-principles calculations, we find that the existence of altermagnetism is determined by the type of interchain magnetic coupling and predict three intrinsic altermagnets, CrBr3, VBr3, and MnBr3, due to their ferromagnetic interchain couplings and five extrinsic ones, CrF3, CrCl3, CrI3, FeCl3, and CoTe3, ascribed to their neglectable or antiferromagnetic interchain couplings. Moreover, the interchain magnetic coupling here is highly tunable by manipulating the interchain spacing, leading to experimentally feasible transitions between altermagnetic and nodal-line semiconducting states. In addition, applying external electric fields can further modulate the spin splitting. Our findings establish a highly tunable family of Q1D altermagnets, offering fundamental insights into the intricate relationship between geometry, electronic structure, and magnetism. These discoveries hold significant promises for experimental realization and future spintronic applications.

Kagome electronic states in gradient-strained  untwisted graphene bilayers

Kagome electronic states in gradient-strained untwisted graphene bilayers

Zeyu Liu, Xianghua Kong, Zewen Wu, Linwei Zhou, Jingsi Qiao and Wei Ji

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.