Two‐dimensional (2D), high‐temperature, half‐metal ferromagnetic semiconductors with large spin gap and topological band structures are highly desirable for novel nanoscale spintronic applications. A family of stable 2D honeycomb‐Kagome Cr2X3 (X=O,S,Se) monolayers is proposed through first‐principles calculations. Buckled Cr2O3 is a ferromagnetic semiconductor with large out‐of‐plane magnetocrystalline anisotropy energy and a predicted Curie temperature of 332 K under moderate biaxial tensile strain. Planar Cr2S3 and Cr2Se3 are ferromagnetic half‐metals with mirror‐symmetry‐protected nodal lines for spin‐down channel and large direct gap (4.59 and 4.76 eV) for spin‐up channel. The Fermi velocities for Cr2S3 and Cr2Se3 are 2.1×105 and 1.5×105 m s−1, respectively, which is comparable with that of silicene, 5.3 × 105 m s−1. Their Berezinskii–Kosterlitz–Thouless transition temperatures are determined to be as high as 445 and 695 K. In addition, their half metallicity can be well maintained on h‐BN nanosheets and is immune to chemical perturbation and mechanical strain. Its fascinating magnetic properties and topological nodal lines render 2D Cr2X3 (X=O,S,Se) suitable for novel spintronic devices and exotic quantum applications.
Using first-principles calculations, we find Li-intercalated bilayer arsenene with AB stacking is dynamically stable, which is different from pristine bilayer with AA stacking. Electron-phonon coupling of the stable Li-intercalated bilayer arsenene are dominated by the low frequency vibrational modes (E″(1), [Formula: see text](1), E'(1) and acoustic modes) and lead to an superconductivity with T = 8.68 K with isotropical Eliashberg function. Small biaxial tensile strain (2%) can improve T to 11.22 K due to the increase of DOS and phonon softening. By considering the fully anisotropic Migdal-Eliashberg theory, T are found to be enhanced by 50% and exhibits a single anisotropic gap nature. In addition, considering its nearly flat top valence band which is favorable for high temperature superconductivity, we also explore the superconducting properties of hole-doped monolayer arsenene under different strains. the unstrained monolayer arsenene superconducts at T = 0.22 K with 0.1 hole/cell doping. By applying 3% biaxial strain, T can be lifted up strikingly to 6.69 K due to a strong Fermi nesting of the nearly flat band. Then T decreases slowly with strain. Our findings provide another insight to realize 2D superconductivity and suggest that the strain is crucial to further enhance the transition temperature.
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