Two-dimensional rectangular tantalum carbide halides TaCX (X = Cl, Br, I): novel large-gap quantum spin Hall insulators

Abstract

Quantum spin Hall (QSH) insulators possess edge states that are topologically protected from backscattering. However, known QSH materials (e.g. HgTe/CdTe and InAs/GaSb quantum wells) exhibit very small energy gap and only work at low temperature, hindering their applications for room temperature devices. Based on the first-principles calculations, we predict a novel family of QSH insulators in monolayer tantalum carbide halide TaCX (X = Cl, Br, and I) with unique rectangular lattice and large direct energy gaps larger than 0.2 eV, accurately, 0.23−0.36 eV. The mechanism for 2D QSH effect in this system originates from a intrinsic d −d band inversion, different from conventional QSH systems with band inversion between s−p or p−p orbitals. Further, stain and intrinsic electric field can be used to tune the electronic structure and enhance the energy gap. TaCX nanoribbon, which has single-Dirac-cone edge states crossing the bulk band gap, exhibits a linear dispersion with a high Fermi velocity comparable to that of graphene. These 2D materials with considerable nontrivial gaps promise great application potential in the new generation of dissipationless electronics and spintronics. KeywordsQuantum spin Hall insulator, Tantalum Carbide Halide, Gapless edge states, Band inversion, First-principles calculations Two-dimensional (2D) topological insulators (TIs), also known as Quantum spin Hall (QSH) insulators, characterized by an insulating bulk and fully spin-polarized gapless helical edge states without backscattering at the sample boundaries, are protected by timereversal symmetry and thus are promising for achieving dissipationless transport devices. 1,2Compared to three-dimensional (3D) TIs with the surface states only projected from exact 180 • C backscattering and suffering from other angles' scattering, the electrons with opposite

Gallium bismuth halide GaBi-X2 (X = I, Br, Cl) monolayers with distorted hexagonal framework: Novel room-temperature quantum spin Hall insulators

“…For the DHF GaBi-I 2 monolayer, the valence and conduction bands meet at a single point along the Γ-X line, giving rise to a distorted Dirac cone, as shown in Figure 3(a). Similar band structures can also be found in other rectangular lattices [97,98]. The orbital-projected band structure without SOC of the DHF GaBi-I 2 monolayer close to the Fermi level is shown in Figure 4(a).…”

Observation of the Weak Antilocalization and Linear Magnetoresistance in Topological Insulator Thin Film Hall Bar Device

“…From the figure it is evident that, there is a decrease in the resistance in the temperature range from 300 to 240 K. The reason, we can consider with the bulk band gap. With the recent report on the ARPES measurements analysis of Bi 2 Se 3 thin film grown on SiC (0001) by MBE [36], where there is a progressive and systematic increase in the bulk band gap with reducing film thickness, it implies the quantum confinement of the film along the growth direction perpendicular to the substrate. As in our case, the grown film is thin enough, so the result is quite practical and evident at higher temperatures.…”

Emerging topological states in quasi‐two‐dimensional materials

“…Figure (c–e) reprinted with permission from Ref , copyright 2015 American Chemical Society. Figure (f–i) reprinted with permission from Ref .…”

“…Recently, Weng et al proposed that the MXene functionalized with oxygen, M 2 CO 2 ( M =W, Mo, and Cr), are QSH insulators with band gaps up to 0.194 eV in W case (Figure (a) and (b)). Combining the strategies of searching topological state in TM carbides and halides, QSH insulators that exhibit energy gaps larger than 0.2 eV were discovered in rectangular tantalum carbide halides TaC X ( X =Cl, Br, I) monolayers (Figure (f)–(i)).…”