The quantum spin Hall (QSH) effect is promising for achieving dissipationless transport devices due to the robust gapless states inside the insulating bulk gap. However, QSH insulators currently suffer from requiring extremely high vacuums or low temperatures. Here, using first-principles calculations, we predict cyanogen-decorated plumbene (PbCN) to be a new QSH phase, with a large gap of 0.92 eV, that is robust and tunable under external strain. The band topology mainly stems from s-p band inversion related to the lattice symmetry, while the strong spin-orbit coupling (SOC) of the Pb atoms only opens a large gap. When halogen atoms are incorporated into PbCN, the resulting inversion-asymmetric PbF(CN) can host the QSH effect, accompanied by the presence of a sizable Rashba spin splitting at the top of the valence band. Furthermore, the Te(111)-terminated BaTe surface is proposed to be an ideal substrate for experimental realization of these monolayers, without destroying their nontrivial topology. These findings provide an ideal platform to enrich topological quantum phenomena and expand the potential applications in high-temperature spintronics.

Two-dimensional multiferroic materials with controllable ferromagnetism and ferroelasticity are an interesting topic and offer unprecedent opportunities for achieving long-sought controllable spintronic devices. However, the reported proposals on hypothetical materials are rarely realized experimentally so far. We perform first-principles calculations to find that the non-dispersive nature of the valence band maximum with a Mexican-hat-like band in monolayer α-PbO can be as a prototype to realize either ferromagnetism or ferroelasticity under p-type doping. Remarkably, a multiferroic phase coexisting with ferromagnetism and ferroelasticity can be obtained for hole densities in the range of 1.22–3.48 × 1014 cm−2. Also, the Curie temperature, structural stability, and exfoliation energy of α-PbO are discussed. These interesting mechanical, electronic, and magnetic properties in α-PbO provide an ideal platform to research physics and high-performance multi-functional devices.

Monolayer Cr2Ge2Te6 (ML-CGT) has attracted broad interest due to its novel electronic and magnetic properties. However, there are still controversies on the origin of its intrinsic magnetism. Here, we systematically...

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Ferrimagnetic half-metal is more promising in spintronic devices than its ferromagnetic counterpart due to its lower stray fields and favorable robustness of magnetism. In comparison to the three-dimensional counterpart, the realization on two-dimensional ferrimagnetic half-metal remains blank up to date. Here, based on first-principles calculations and Monte Carlo simulations, we predict a ferrimagnetic half-metallicity in two-dimensional MXene Mo3N2F2 with a Curie temperature of 237 K and a considerable magnetic anisotropy energy. The ferrimagnetic coupling is mainly from the interactions of itinerant d electron between different Mo layers, and thus endows a 100% spin-polarization at the Fermi level with a sizable half-metallic gap of 0.47 eV. Such ferrimagnetic half-metallicity is also robust against external strains. Additionally, diverse magnetic and electronic characters can be controlled, depending on a differently terminated Mo3N2F2 surface. These findings provide an ideal platform to design spintronic devices related to two-dimensional ferrimagnetic half-metals.