Robust large-gap quantum spin Hall insulators in methyl-functionalized III-Bi buckled honeycombs

Abstract

Based on first-principles calculations, we predict that the methyl-functionalized III-Bi monolayers, namely III-Bi-(CH 3 ) 2 (III=Ga, In, Tl) films, own quantum spin hall (QSH) states with band gap as large as 0.260, 0.304 and 0.843 eV, respectively, making them suitable for room-temperature applications. The topological characteristics are confirmed by s-p x,y band inversion, topological invariant Z 2 number, and the time-reversal symmetry protected helical edge states. Noticeably, for GaBi/InBi-(CH 3 ) 2 , the s-p x,y band inversion occurred in the progress of spin-orbital coupling (SOC), while for TlBi(CH 3 ) 2 , the s-p x,y band inversion happened in the progress of chemical bonding. Significantly, the nontrivial topological states in III-Bi-(CH 3 ) 2 films are robust against the mechanical strain and various methyl coverage, making them particularly flexible to substrate choice for device applications. Besides, we find the h-BN is an ideal substrate for III-Bi-(CH 3 ) 2 films to realize large gap nontrivial topological states. These findings demonstrate that the methyl-functionalized III-Bi films may be good QSH effect platforms for topological electronic devices design and fabrication in spintronics.

Large Gap Two-Dimensional Topological Insulators with the Significant Rashba Effect in Ethynyl and Methyl Functionalized PbSn Monolayers

“…However, hydrogenation and fluorination were recently reported to give rise to a rapid increase of lattice disorders and defects . Thus, the attention has switched to using small molecules to decorate films. − Ethynyl and methyl are excellent options for modifying the surfaces to achieve large gaps with geometric stability. In addition, heavy elements like Pb and Sn are usually accompanied by strong SOC, which favors the formation of TIs with enormous bandgaps.…”

Intrinsic Room-Temperature Ferromagnetism in New Halide Perovskite AgCrX3 (X: F, Cl, Br, I) Using Ab Initio and Monte Carlo Simulations

“…Modern spintronic applications, which include GMR, MRAM, spin valves, and magnetic sensors, effectively utilize half-metallic (HM) ferromagnetic materials as a result of recent improvements in spintronic innovation. , De Groot et al, discovery of half-metallic ferromagnetism in (Pt/Ni)­MnSb Heusler alloys for the first time in 1983 opened up an entirely novel area for research . Since then, the phenomenon of HMF in spinel chalcogenides, along with single and DPs, has been the topic of extensive theoretical and experimental research. , Binary and ternary oxides, such as MgO, CaO, ZnO, SrTiO 2 , BeO, SiO 2 , and other compounds, , have been found to demonstrate magnetism.…”

Large gap two-dimensional topological insulators with the coexistence of a significant Rashba effect and piezoelectricity in functionalized PbGe monolayers

“…However, fluorination and hydrogenation were recently revealed to give rise to a rapid increase of defects and lattice disorder, 13 which severely inhibits their practical application prospects. Thus, small molecule functionalization, with groups such as cyano (–CN), 14 ethynyl (–C 2 H), 15 amidogen (–NH 2 ), 16 methyl (–CH 3 ) 17 etc ., becomes a more desirable alternative to achieve QSH states with a stable lattice structure and large topological bandgaps, and is being widely used to predict new ideal QSH insulators.…”