Two-dimensional MX Dirac materials and quantum spin Hall insulators with tunable electronic and topological properties
- PDF / 2,102,564 Bytes
- 6 Pages / 612 x 808 pts Page_size
- 101 Downloads / 204 Views
iversity Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 12 June 2020 / Revised: 28 July 2020 / Accepted: 29 July 2020
ABSTRACT We propose a novel class of two-dimensional (2D) Dirac materials in the MX family (M = Be, Mg, Zn and Cd, X = Cl, Br and I), which exhibit graphene-like band structures with linearly-dispersing Dirac-cone states over large energy scales (0.8–1.8 eV) and ultra-high Fermi velocities comparable to graphene. Spin-orbit coupling opens sizable topological band gaps so that these compounds can be effectively classified as quantum spin Hall insulators. The electronic and topological properties are found to be highly tunable and amenable to modulation via anion-layer substitution and vertical electric field. Electronic structures of several members of the family are shown to host a Van-Hove singularity (VHS) close to the energy of the Dirac node. The enhanced density-of-states associated with these VHSs could provide a mechanism for inducing topological superconductivity. The presence of sizable band gaps, ultra-high carrier mobilities, and small effective masses makes the MX family promising for electronics and spintronics applications.
KEYWORDS two-dimensional, Dirac materials, density functional theory, topological properties
1
Introduction
The presence of Dirac-cone structures and singularities in the electronic energy spectra of functional materials can endow them with unique properties and promising prospects for both fundamental research and applications [1]. The discovery of graphene, a monolayer honeycomb structure composed of carbon atoms [2], has spurred intense interest in the exotic physics associated with massless fermions, half-integer [3, 4]/fractional [5, 6]/fractal [7–9] quantum Hall effects (QHE), quantum spin Hall effect (QSH) [10] and other novel phenomena and properties [11, 12]. Within the vast space of inorganic twodimensional (2D) compounds [13–17], graphene [3, 4, 18], silicene and germanene [19], graphynes [20, 21], and other related systems have been predicted to be Dirac materials [1, 22]. Dirac cones have been unambiguously confirmed by experiment in graphene. Experimental identification of Diraccone structure in silicene and germanene is still controversial [23–25], where appropriate substrates are needed to preserve the coherence of the Dirac cones. Experimental progress toward identifying Dirac states in more complex 2D structures, such as the graphynes, is still in its infancy [26]. It is therefore highly desirable to continue the search for novel 2D Dirac systems. Considering the various requirements associated with crystal
symmetries and chemical orbital interactions, it is a challenging task to search for novel 2D systems hosting Dirac cones close to the Fermi energy. Within the framework of tight-binding approximations, the occurrence of Dirac cone is driven by the presence of appropriate combinations of hopping energies [27, 28], which are controlled by details of the atomic geometries and the types of 2D crystal lattices inv
Data Loading...
