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The physical properties induced by layer stacking in two dimensional materials are fascinating. Here, a hexagonal Kagome lattice V2Se3 is constructed to investigate the dependence of the quantum anomalous Hall effect (QAHE) and the phase transition on the different stacking. Based on first principles calculations, the tight-binding model, and the irreducible representations, it is found that QAHE with a Chern number of 1 can be realized in the V2Se3 monolayer. While the V2Se3 bilayer is constructed, the interlayer interaction affects the Dirac cone, so QAHE with Chern number changes from −1 to 2 can be obtained by changing the different stacking patterns. On the other hand, applying biaxial tensile strain and changing stacking patterns in the V2Se3 bilayer will affect the d orbitals of the V atoms. In bilayer V2Se3, applying biaxial tensile strain affects the d orbitals of the V atoms that constitute the Dirac cone, and then a topological phase transition appears. Moreover, changing the stacking patterns induces the hybridization competition of the d orbitals, which leads to a magnetic phase transition. Constructing a Kagome bilayer and changing their stacking patterns paves a pathway in exploring quantum effects of topology and magnetism in layered materials. [ABSTRACT FROM AUTHOR]

Kagome materials serve as crucial platforms for investigating the quantum anomalous Hall effect (QAHE) due to the presence of kagome bands in their electronic structures. However, despite the theoretical predictions being proposed, kagome band material realizations have been limited. In this work, through tight-binding (TB) model analysis, by setting the nearest-neighbor hopping integrals with opposite signs, we propose a Yin–Yang kagome band structure characterized by two stable enantiomorphic kagome bands. Furthermore, we design a monolayer V3Cl6 to confirm the TB model. Three V atoms are located in different coordination environments in V3Cl6, so opposite signs of the hopping integrals between two of their orthogonal d orbitals can be achieved, which is the key to realize Yin–Yang kagome band structures. The calculated band structures obtained from first principles are consistent with those from the TB model. Additionally, we find that the two enantiomorphic flat bands in monolayer V3Cl6 possess opposite Chern number after spin–orbit coupling is considered, which can also be confirmed from symmetry index analysis. The Chern numbers as well as the topological properties can be modulated by doping hole or adjusting the magnetization directions, so the QAHE can be tuned in monolayer V3Cl6. Our results provide a practicable pathway for realizing Yin–Yang kagome band structures and achieving tunable QAHE in them. [ABSTRACT FROM AUTHOR]

Two-dimensional intrinsic magnetic topological materials that can realize device miniaturization have attracted significant attention recently based on their chiral dissipationless edge states. However, since the experimental observation of quantum anomalous Hall effect (QAHE) is still limited by low temperature, high operating temperature and large nontrivial gap are urgently needed. Here, monolayer MnAsO3 is predicted to be a room-temperature intrinsic magnetic topological material with high Chern number C = 3 based on first-principles calculations, which offers the possibility of achieving high-speed and low-energy-consumption electron transport in the future. Furthermore, the large and experimental feasible nontrivial gap up to 79.09 meV is obtained under compressive strain modulation. Moreover, the high-Chern-number topological phase transition and strain-induced spin-unlocked edge states are observed, indicating the possibility of tuning the electron transport of QAHE. All these findings suggest that monolayer MnAsO3 is a suitable and promising material for fabricating low-energy-consumption spintronics devices. [ABSTRACT FROM AUTHOR]

With the Su–Schrieffer–Heeger model and Green's function method, the length dependence of magnetoresistance in organic spin valves is calculated in the frame of tunneling transport. Based on different energy level alignments between the molecule and the electrodes, the length effect on the magnetoresistance is investigated in three transport schemes, barrier tunneling, resonant tunneling, and transition between them. In the first scheme, a length-induced exponential or linear decline of the magnetoresistance is obtained. An oscillation and nonlinear dependence are observed in the second and third schemes. The mechanism is explained by investigating the transmission spectra at different lengths, where the evolution of the efficient transmission in the bias window with length differs in different schemes. The results agree with many experimental measurements qualitatively. [ABSTRACT FROM AUTHOR]

The exploration of valley-related physics is essential to the development and refinement of valleytronics. Here, a paradigm called chiral breathing-valley locking (CBVL) is proposed, in which two chiral "breathing" phases are completely locked to their valley indexes. Utilizing first-principles calculations, a two-dimensional (2D) kagome lattice with large spontaneous valley polarization (VP), namely, monolayer Ta3I8, is proposed to realize CBVL. There are two breathing phases with chiral symmetry in Ta3I8, and they can change to each other under some conditions. The valley indexes change between "−K" and "K" along the breathing of the two chiral symmetric phases, so CBVL can be obtained. Remarkably, the VP is up to 199.7 meV, so CBVL can cause the obvious switching of the anomalous valley Hall effect (AVHE). Additionally, a 2D Janus Kagome structure TaI4X4 is constructed to confirm experimentally the feasibility of electric field modulation on the CBVL. The built-in electric field and the breathing mode can mutually influence each other in TaI4X4, which provides a synergistic regulation of the AVHE. Our findings broaden the horizon for exploring AVHE materials and provide a platform for future valleytronic applications. [ABSTRACT FROM AUTHOR]

Hydrogen energy is very important as a new clean energy source to combat the growing environmental problems. In this regard, novel photocatalyst materials for water splitting have a wide range of applications. Using first principles calculations, we theoretically studied three orthorhombic group-IVB nitride halide monolayers, Hf2N2Br2, Janus HfZrN2Br2 and Janus Hf2N2ClBr. The energy, dynamic and thermal stabilities are demonstrated for all three monolayers. Using the HSE hybrid functional, the calculations reveal that they are direct band gap semiconductors with suitable band edge positions, good optical absorptions, and anisotropic carrier mobilities, which makes them promising for water splitting applications. Importantly, the photogenerated carriers provide enough driving force to trigger the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) within wide pH ranges, and then overall water splitting can be achieved spontaneously. We conclude that orthorhombic group-IVB nitride halide monolayers have potential applications in photocatalytic nanodevices. [ABSTRACT FROM AUTHOR]