Stable two-dimensional dumbbell stanene: A quantum spin Hall insulator

Abstract

From density functional theory within the generalized gradient approximation we predict a structure of stanene with dumbbell units (DBs), and show that it is a two-dimensional topological insulator with an inverted band gap which can be tuned by compressive strain. Furthermore, we propose that the boron nitride sheet and reconstructed (2×2) InSb(111) surfaces are ideal substrates for the experimental realization of DB stanene, maintaining its nontrivial topology. Combined with standard semiconductor technologies, such as magnetic doping and electrical gating, the quantum anomalous Hall effect, Chern half metallicity, and topological superconductivity can be realized in DB stanene on those substrates. These properties make the two-dimensional supported stanene a good platform for the study of quantum spin Hall insulators as well as other exotic quantum states of matter. , have attracted much attention in recent decades due to their exotic electronic properties. Especially for twodimensional (2D) graphene, its great success has inspired the "graphene age" in the fields of physics, chemistry, and material science. For direct integration on silicon based electronic devices, the search for other 2D group IV materials has triggered enormous interest. Since the first proposal of low-buckled (LB) silicene [5], a dumbbell configuration of silicene [6] and a flat germanene structure [7] have been synthesized. In contrast to graphene and LB silicene, the bond lengths in LB 2D layers of tin (called stanene) are much larger, and the relatively weak π -π bonding cannot stabilize the planar configuration, resulting in instability of free-standing LB stanene (see the Supplemental Material [8] for details).Following the initial discovery of the quantum spin Hall (QSH) effect in 2D topological insulator (TI) HgTe quantum wells [9,10], much attention has been focused on the search for 2D TIs with larger energy gaps. Recently 2D stanene has been proposed as a promising material to realize the QSH insulator, with gaps as large as 0.3 eV, with appropriate chemical functionalization [11]. Owing to time-reversal (TR) symmetry, spin-filtered helical edge states propagate along the edges with dissipationless spin and charge currents, leading to promising potential applications in spintronics and fault-tolerant quantum computation [12].In this Rapid Communication, we propose a structure of stanene with dumbbell units (DBs) (free-standing or supported on an insulating substrate). Based on ab initio structure optimization, phonon dispersion, and band structure calculations, we predict that this structure can be stable and behave as a 2D TI. The band inversion induced by spin-orbit coupling * Corresponding author: dwh@phys.tsinghua.edu.cn † Corresponding author: angel.rubio@ehu.es (SOC) occurs at the point and the gap size can be tuned by applying compressive strain. We further show that in the realistic growth on the substrate, for example, the boron nitride (BN) sheet or reconstructed InSb(111) surface on which α-tin(111) thin films have b...

Large-gap quantum spin Hall states in decorated stanene grown on a substrate

“…The combined effects would lead to distinct electronic structures for ultrathin materials like stanene. The important influence of substrate, however, has been largely ignored in previous works [5][6][7][8][9][10][11][12][13][14][15][16]. Realizing large-gap QSH states in ultrathin materials grown on substrate emerges as a challenging issue.…”

“…Generally, when growing stanene on other substrates, it is possible to get type-II and type-III energy level alignments [33] as well. Band inversion may occur between stanene states and substrate states [8], which could also induce QSH states. Furthermore, the use of magnetic substrates, like EuTe(111), may induce band inversion for one spin channel only, giving rise to novel QAH states.…”

“…A few large-gap QSH insulators have been theoretically proposed [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], predominantly in ultrathin materials of free-standing form. Among them, stanene, the graphene counterpart of tin (Sn), is of special interest [5].…”

Prediction of a two-dimensional S3N2 solid for optoelectronic applications

“…This epic discovery has opened up the possibility of isolating and studying the intriguing properties of a whole family of 2D materials including the 2D insulator boron nitride (BN) [2][3][4], graphane analogues of group IV elements, i.e. semimetallic silicene, germanene, and stanene [5][6][7][8][9][10][11], 2D transition-metal dichalcogenides [12][13][14][15][16], such as molybdenum disulfide [2,17,18] and tungsten disulfide [19], and very recently, 2D phosphorus, i.e. phosphorene [20], which extend the 2D material family into the group V. These 2D free-standing crystals exhibit unique and fascinating physical and chemical properties that differ from those of their 3D counterparts [21,22], opening up possibilities for numerous advanced applications.…”

Z2Invariance of Germanene onMoS2from First Principles

“…Both silicene (Si) and germanene "buckle" with the two sublattices moving in opposite directions out of the original plane but maintaining inversion symmetry [16][17][18]; stanene (Sn) forms a different dumbell structure [19]. The unsupported layers are predicted to be TIs [19,20]. Experimental efforts have so far focussed on growing silicene [21] and germanene [14] on metallic substrates where the intrinsic transport properties cannot be studied.…”