No abstract

Based on the density functional theory method in combination with the nonequilibrium green's function formalism, the quantum transport properties in graphene-[Formula: see text] vertical heterojunction were investigated in this work. The leads are boron doped graphene and seamlessly connect to the graphene nanoribbon in central scattering region. Although there is a weak graphene-[Formula: see text] interaction, molybdenum disulfide can smooth the electrostatic potential and enlarge the transport properties of the whole device. However, another competitive factor is that of the edge states of the [Formula: see text] nanoribbon. When the transport is along the zigzag direction of graphene, the armchair [Formula: see text] nanoribbon simply enlarges the transmission coefficient. Nevertheless, in the armchair transport system, there is an asymmetric electrostatic potential induced by the different atomic potentials of S and Mo atoms at both edges in the zigzag [Formula: see text] nanoribbon, whose potential can lead to obvious scattering from graphene to [Formula: see text] and suppress the transmission probability. Therefore, it also suppresses the influence of zigzag [Formula: see text] nanoribbon on the transmission coefficient. Our first principles simulations provide useful predictions for the application of graphene based emerging electronics, which may stimulate further experimental exploration.

Half-metallic nodal loops robust against spin–orbit couplings are realized in covalent–organic Cr2N6C3 monolayers. Type I, II, and III nodal loops, protected by a mirror symmetry, are found coexisting in the material.

Two-dimensional (2D) topological insulators, a type of the extraordinary quantum electronic states, have attracted considerable interest due to their unique electronic properties and promising potential applications. Recently, the successful fabrication of 2D Te monolayers (i.e. tellurene) in experiments (Zhu et al., Phys Rev Lett 119:106101, 2017) has promoted researches on the group-VI monolayer materials. With first-principles calculations and tight-binding (TB) method, we investigate the structures and electronic states of 2D polonium (poloniumene), in which Po is a congener of Te. The poloniumene is found to have the tendency of forming a three-atomic-layer 1 T-MoS2-like structure (called trigonal poloniumene), namely, the central-layer Po atoms behave metal-like, while the two-outer-layer Po atoms are semiconductor-like. This unique multivalent behavior of the Po atoms is conducive to the structural stability of the monolayer, which is found to be an intrinsic quantum spin Hall insulator with a large band gap. The nontrivial topology originates from the $$p_{x,y} - p_{z}$$ p x , y - p z band inversion, which can be understood based on a built TB model. The poloniumene with different congener elements doped is also explored. Our results provide a thorough understanding of structures and electronic states of 2D polonium-related materials.

Abundant topological states, including triply degenerate point semimetals and Dirac semimetals, are achieved in the layered SnPbH2 crystals built based on monolayer SnPbH2 with different stacking patterns.