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The valley-polarized quantum anomalous Hall (VP-QAH) materials, which combine valley polarization and the quantum anomalous Hall (QAH) effect, are of both fundamental and technological importance due to their potential applications for nanoscale devices. Here, we explored the stability, magnetic, and topological properties of two-dimensional MnTiX2 (X = F/Cl/Br) monolayers based on first-principles calculations. Our results show that all the structures have robust antiferromagnetic orders with large magnetic anisotropic energies and high transition temperatures (480–670 K). In the absence of spin–orbital coupling (SOC), the MnTiX2 monolayers represent antiferromagnetic quadratic crossing semimetals. In the presence of SOC, the quadratic crossing points of the systems are opened with sizable bandgaps (> 0.5 eV), and they are transformed to be QAH insulators with |C| = 1. Moreover, the MnTiF2 monolayer is found to be a spontaneous VP-QAH semiconductor due to the time reversal symmetry and inversion symmetry being broken. These insights provide an ideal platform for achieving VP-QAH materials for dissipationless transport and quantum computing. [ABSTRACT FROM AUTHOR]

Although much efforts have been made into exploration of quantum anomalous Hall (QAH) effects in theory and experiment, the QAH materials with high Chern number are still rare to people. Here, by first-principles calculations, we theoretically predicted stable 2D robust QAH monolayers, Ti3X5 (X = S, Se) with high Chern number |C| = 2. In the absence of spin–orbital coupling (SOC), the ferromagnetism polarizes the system into a half semimetal with eight Weyl points in the whole Brillouin zone. When SOC is turned on, the bandgap is opened with two chiral edge modes. Additionally, a topological phase transition from C = −2 to C = 2 is realized by rotating the magnetization direction from z axis to −z axis. In addition, a phase transition from C = −2 to C = 0 can be manipulated by applying external strains or varying electronic correlation Ueff. Our work provides potential high Chern number QAH candidates for the practical electronic application. [ABSTRACT FROM AUTHOR]

The development of quantum anomalous hall (QAH) insulator with high transition temperature is the key to realize practical applications in future quantum technology and spintronics. Here, we predicted two stable two-dimensional kagome structures, Ti3Te4 and Cr3Te4, and found that both of them are intrinsic QAH insulators, using density functional theory calculations. In the absence of spin–orbit coupling (SOC), both systems display ferromagnetism (FM) Weyl semimetal states. Remarkably, Ti3Te4 monolayer is revealed to be a robust ferromagnetic half metal with high Curie temperature (TC) of 403 K. When the SOC effect occurs, it spontaneously creates QAH states with large nontrivial bandgap and chiral edge states. As a result, the Ti(Cr)3Te4 monolayer is changed to be QAH insulators with Chern number C = ±1 by rotation of magnetization orientation. In addition, the phase change from FM QAH insulator to antiferromagnetic insulator can be manipulated by applying external strains. Moreover, a high-Chern number phase (C = 2) arises by building Ti3Te4/MoS2/Ti3Te4 heterostructure. Meanwhile, the topological phase transition can be well recurred by using a spinless three-band tight-binding (TB) model. The findings present ways to realize potential QAH insulators with high transition temperatures. [ABSTRACT FROM AUTHOR]

Searching for two-dimensional materials combining both magnetic order and topological order is of great significance for quantum devices and spintronic devices. Here, a class of two-dimensional transition metal borides, TM2B3 (TM = Ti–Ni), with high stability and stable antiferromagnetic (AFM) orders was predicted by using the first-principles method. The result shows that they possess large magnetic anisotropy energy and high critical temperature. Interestingly, Mn2B3 monolayer is confirmed to be AFM Dirac node line semimetal with several Dirac points near the Fermi level. Detailed analysis of the irreducible representations shows that the nodal lines are protected by the horizontal mirror symmetry Mz. Our findings provide an excellent platform for exploring topological and magnetic materials ready for the next generation of spintronic devices. [ABSTRACT FROM AUTHOR]

The electrochemical nitrogen reduction reaction (eNRR) to NH 3 has become an alternative to traditional NH 3 production techniques, while developing NRR catalysts with high activity and high selectivity is of great importance. In this study, we systematically investigated the potentiality of dual transition metal (TM) atom anchored electrocatalysts, TM 1 TM 2 @C 9 N 4 (TM 1 , TM 2 = 3(4)d TM atoms), for the NRR through the first principles high-throughput screening method. A total of 78 TM 1 TM 2 @C 9 N 4 candidates were designed to evaluate their stability, catalytic activity, and selectivity for the NRR. Four TM 1 TM 2 @C 9 N 4 candidates (TM 1 TM 2 = NiRu, FeNi, TiNi, and NiZr) with an end-on N 2 adsorption configuration, and two candidates (TM 1 TM 2 = TiNi and TiFe) with a side-on adsorption configuration, were screened out with the advantage of suppressing the hydrogen evolution reaction (HER) and exhibiting high NRR activity. Moreover, the catalysts with end-on and side-on N 2 adsorption configurations were determined to favor distal and consecutive reaction pathways, respectively, with favorable limiting potentials of only -0.33 V to -0.53 V. Detailed analysis showed that the N 2 adsorption and activation are primarily ascribed to the strong back-donation interactions between the d-electrons of TM atoms and the anti-orbitals of an N 2 molecule. Our findings pave a way for the rational design and rapid screening of highly active C 9 N 4 -based catalysts for the NRR.