Based on first-principles density functional theory calculations, we systemically study the properties of two-dimensional buckled single-layer bismuth (b-bismuthene). The structure, stability, and electronic properties are mainly discussed by PBE + SOC method and the hybrid functional HSE06 method is used to further revise the band gap. The optimized b-bismuthene is determined to be dynamically and thermally stable with an indirect band gap. In particular, there is a peculiar Rashba spin-splitting emerging in the valence band maximum (VBM) states. Interestingly, the Rashba energy could be effectively modulated by in-layer biaxial strain. By applying in-layer biaxial strain, one can find that b-bismuthene has indirect–direct band gap and semiconductor–semimetal transitions. Moreover, we also study the electronic structure of bilayer b-bismuthene that is sensitively dependent on the interlayer distance. We demonstrate that the electric field (E-field) leads to a breaking of the Rashba-type splitting near the VBM of single b-bismuthene. More importantly, there is a synergistic effect when both strain and electric field are applied at the same time. The E-field induced band splitting character could be modified by the strain strength. Thus, this study indicates that b-bismuthene may be a potential material in both electronic and spintronic devices.

We predict, through first-principles calculations, a different class of Janus two-dimensional (2D) materials $X{\mathrm{Sn}}_{2}Y$ ($X, Y=\mathrm{P}$, As, Sb, and Bi; $X\ne Y$). It has found that these 2D monolayers have intrinsic polarization effect owing to presence of mirror-symmetry breaking. $\mathrm{Sb}{\mathrm{Sn}}_2\mathrm{Bi}, \mathrm{As}{\mathrm{Sn}}_2\mathrm{Sb}$, and $\mathrm{P}{\mathrm{Sn}}_2\mathrm{As}$ have a semiconducting feature, however $\mathrm{As}{\mathrm{Sn}}_2\mathrm{Bi}, \mathrm{P}{\mathrm{Sn}}_2\mathrm{Bi}$, and $\mathrm{P}{\mathrm{Sn}}_2\mathrm{Sb}$ have a metallic feature with inverted band structure. When the spin-orbit coupling (SOC) is considered, the double Rashba effects are found in $\mathrm{Sb}{\mathrm{Sn}}_2\mathrm{Bi}$. Band inversion coupling with SOC leads to unexpected spin-valley splitting characteristics in $\mathrm{As}{\mathrm{Sn}}_2\mathrm{Bi}, \mathrm{P}{\mathrm{Sn}}_2\mathrm{Bi}$, and $\mathrm{P}{\mathrm{Sn}}_2\mathrm{Sb}$, showing a circle-type Berry curvature. The electronic and spin properties of Janus $X{\mathrm{Sn}}_{2}Y$ monolayers are tunable via applying external strain and electric field, resulting in Rashba-type spin-splitting, $p_z/p_{xy}$ band inversion, and a Dirac cone. In particular, the sombrero band dispersion and Van Hove singularity are revealed in $\mathrm{P}{\mathrm{Sn}}_2\mathrm{As}$ by exerting tensile strain. We therefore investigate the Lifshitz transition and inverse Edelstein effect (also referred as spin-charge conversion) of the strained $\mathrm{P}{\mathrm{Sn}}_2\mathrm{As}$. On the basis of the k·p model in the clean limit, the Drude coefficient for spin-charge conversion is estimated to be about 0.086 $e$/Å as tensile strain of +3%. Finally, the synergic effect of tensile strain and electric field is considered to manipulate the spin-charge conversion. Our results provide a class of 2D materials to investigate the Rashba effect, Lifshitz transition, and spin-charge conversion.

As the isoelectronic counterpart of phosphorene, monolayer group IV–VI binary MX (M = Ge, Sn; X = Se, S) compounds have drawn considerable attention in recent years.

Recently, MA ₂ Z ₄ materials have received tremendous attention due to their amazing electronic, spintronic, and optoelectronic properties.

Using first-principles calculations, a class of Janus two-dimensional materials, $\mathrm{P}{A}_2\mathrm{As}$ ($A=\mathrm{Si}$, Ge, Sn, and Pb) monolayers, is predicted to be dynamically and thermally stable. The band gap of $\mathrm{P}{A}_2\mathrm{As}$ can be linearly modulated by external strain and electric field. The presence of the peculiar sombrero-type band in strained $\mathrm{P}{A}_2\mathrm{As}$ results in the intraband Lifshitz transition near the valence band top when including Rashba spin-orbit coupling. The energy range of intraband Lifshitz transition is linearly dependent on electric field, indicating potential electric control of the Fermi surface properties. In particular, hole doping leads to the ferromagnetic transition in $\mathrm{P}{A}_2\mathrm{As}$ due to Van Hove singularity and a divergence with $1/\sqrt{E}$ of the density of states. This ferromagnetism can be understood in terms of the Stoner criterion $D$($E_{\mathrm{F}}$)$I_{\mathrm{S}}>1$. A saturated magnetic moment of $1{\mu }_{\mathrm{B}}/\mathrm{hole}$ is obtained in hole-doped ${\mathrm{PSn}}_2\mathrm{As}$ and ${\mathrm{PPb}}_2\mathrm{As}$ with a wide range of hole densities. The highest Curie transition temperature $T_{\mathrm{c}}$ is estimated to be 93.5 K at the mean field level. We demonstrate that hole density and tensile strain are two effective approaches to control the Stoner ferromagnetism in practical applications. Moreover, various electronic transitions, such as semiconductor to half-metal, half-metal to metal, and semiconductor to metal, are revealed in hole-doped $\mathrm{P}{A}_2\mathrm{As}$. Finally, we explore the feasibility of realizing ferromagnetism by introducing $p$-type dopants and defects. The experimentally controlled intraband Lifshitz transition and Stoner ferromagnetism demonstrate that Janus $\mathrm{P}{A}_2\mathrm{As}$ monolayers have a wide application potential in future electronic and spintronic devices.

To utilize arsenene as the electronic and spintronic material, it is important to enrich its electronic properties and induce useful magnetic properties in it. In this paper, we theoretically studied the electronic and magnetic properties of arsenene functionalized by 3D transition-metal (TM) atoms (TM@As). Although pristine arsenene is a nonmagnetic material, the dilute magnetism can be produced upon TM atoms chemisorption, where the magnetism mainly originates from TM adatoms. We find that the magnetic properties can be tuned by a moderate external strain. The chemisorption of 3D TM atoms also enriches the electronic properties of arsenene, such as metallic, half-metallic, and semiconducting features. Interestingly, we can classify the semiconducting feature into three types according to the band-gap contribution of spin channels. On the other hand, the chemisorption properties can be modified by introducing monovacancy defect in arsenene. Present results suggest that TM-adsorbed arsenene may be a promising candidate for electronic and spintronic applications.