Two-dimensional spin–valley-coupled Dirac semimetals in functionalized SbAs monolayers

Abstract

In the presence of spin-orbit coupling (SOC), achieving both spin and valley polarized Dirac state is significant to promote the fantastic integration of Dirac physics, spintronics and valleytronics. Based on ab initio calculations, here we demonstrate that a class of spin-valley-coupled Dirac semimetals (svc-DSMs) in the functionalized SbAs monolayers (MLs) can host such desired state. Distinguished from the graphene-like 2D Dirac materials, the Dirac cones in svc-DSMs hold giant spin-splitting induced by strong SOC under inversion symmetry breaking. In the 2.3% strained SbAsH 2 ML, the Dirac fermions in inequivalent valleys have opposite Berry curvature and spin moment, giving rise to Dirac spin-valley Hall effect with constant spin Hall conductivity as well as massless and dissipationless transport. Topological analysis reveals that the svc-DSM emerges at the boundary between trivial and 2D topological insulators, which provides a promising platform for realizing the flexible and controllable tuning among different quantum states.The rise of graphene 1-3 has inspired significant efforts in searching for other 2D Dirac materials (DMs) 4-10 with linear energy dispersion. As the host of massless Dirac fermions, 2D DMs have become the playground for investigating many quantum relativistic phenomena [11][12][13] in the emerging field of Dirac physics. Like graphene, without considering spin-orbit coupling (SOC), the Dirac points in these 2D DMs are protected by symmetry. However, the presence of SOC will open a global bulk gap at the Dirac points and introduce the topologically protected gapless edge states. [13][14][15] Therefore, 2D DMs are formally a quantum spin Hall insulator 13 under time-reversal symmetry [ Fig. 1(a)] or quantum anomalous Hall insulator 12 with time-reversal breaking [ Fig. 1(b)]. In a pioneering theoretical study, Yong and Kane 16 employed symmetry analysis and a two-site tight-binding model to examine the possibility that the Dirac points can not be gapped by SOC [ Fig. 1(c)]. They concluded that nonsymmorphic space group symmetry plays an essential role in protecting the 2D Dirac points against SOC, named as spin-orbit Dirac points (SDPs). Although the first realistic 2D material hosting SDPs was predicted recently 17 , its SDPs are not located at the Fermi level and its Dirac dispersion is contaminated by some extraneous non-Dirac bands. Hence, how to achieve a 2D Dirac semimetal hosting SDPs with clean Dirac bands at the Fermi level remains a great challenge.On the other hand, the discovery of valley-dependent effects in MoS 2 monolayer 18,19 without inversion symmetry aroused an upsurge in the field of 2D valleytronics. 20 For hexagonal 2D materials such as graphene and monolayer group-VI transition metal dichalcogenides, the conically shaped valleys at +K and -K 4 FIG. 1. Schematic electronic band structures without SOC (left) and with SOC (right) for different 2D Dirac materials: (a) quantum spin Hall insulator, (b) quantum anomalous Hall insulator, (c) symmetry-protected Dirac semim...

2D V‐V Binary Materials: Status and Challenges

“…Right: the edge states of semi‐infinite SbAsH 2 monolayer. Reproduced with permission . Copyright 2019, Royal Society of Chemistry.…”

“…The Rashba splitting of the Bi‐terminated heterostructure is stronger than that of the Sb‐terminated heterostructure because of the stronger SOC effect of Bi. Another V‐V binary material, SbAs monolayer, after functionalized with H and halogen atoms, possesses both spin and valley polarized Dirac states (called SbAsX 2 , as shown in Figure b) . Its strong SOC effect results in a giant spin splitting with inversion symmetry breaking.…”

Anisotropic In‐Plane Ballistic Transport in Monolayer Black Arsenic‐Phosphorus FETs

“…For silicon‐based semiconductors, it is difficult to meet International Technology Roadmap for Semiconductors (ITRS) requirements 1. In the Post‐Moore era, 2D semiconductor materials have received extensive attention 2–5. Taking the advantages of natural passivation and gate electrostatics, 2D electronic devices have gained prominence in recent years for next‐generation integrated electronics and optoelectronics applications,6,7 for example, graphene,8 transition metal dichalcogenides (TMDs),9–11 InSe,12–14 pnictogen,15–20 and Bi 2 O 2 Se 21–23…”

Band engineering of Dirac materials in SbmBin lateral heterostructures

“…Recently, nanomaterials formed by group VA elements such as phosphorene, arsenene, antimonene, and bismuthene have emerged as a novel type of 2D materials, which exhibit intriguing structures and properties, leading to a wide range of applications in electronics and optoelectronics. [24][25][26][27] Phosphorene is the rst material in this family; recently, it was mechanically isolated from bulk phosphorus and has already been used to fabricate transistors. 28,29 Unfortunately, phosphorene is very unstable and is rapidly oxidized by the atomic layer deposition process.…”