Growth of Sn thin films on CdTe(111)

152

Quantum spin Hall (QSH) effect is promising for achieving dissipationless transport devices which can be achieved only at extremely low temperature presently. The research for new large-gap QSH insulators is critical for their realistic applications at room temperature. Based on first-principles calculations, we propose a QSH insulator with a sizable bulk gap as large as ∼0.22 eV in stanene film functionalized with the organic molecule ethynyl (SnC 2 H), whose topological electronic properties are highly tunable by the external strain. This large-gap is mainly due to the result of the strong spinorbit coupling related to the p xy orbitals at the Γ point of the honeycomb lattice, significantly different from that consisting of the p z orbital as in free-standing group IV ones. The topological characteristic of SnC 2 H film is confirmed by the Z 2 topological order and an explicit demonstration of the topological helical Dirac type edge states. The SnC 2 H film on BN substrate is observed to support a nontrivial large-gap QSH, which harbors a Dirac cone lying within the band gap. Owing to their high structural stability, this two-dimensional large-gap QSH insulator is promising platforms for topological phenomena and new quantum devices operating at room temperature in spintronics.

“…The SOC is included in the self-consistent calculations of electronic structure. The phonon spectra are calculated using a supercell approach within the PHONON code [37].…”

Section: Computational Methods and Detailsmentioning

confidence: 99%

Ethynyl-functionalized stanene film: a promising candidate as large-gap quantum spin Hall insulator

Zhang

et al. 2015

152

“…The origin of the topological state was ascribed to band inversion of the Sn/Ge spin-down s-p z bands [24]. In experiments, Sn ultrathin films with a buckled honeycomb lattice have been fabricated with molecular beam epitaxy techniques [25][26][27], making the experimental observation of the QAH effect in the 2D Sn films step forward. Thus, the systems, especially stanene, should be excellent candidates to be employed to observe QAH effects in experiments at a relatively high temperature.…”

Section: Introductionmentioning

confidence: 99%

Quantum anomalous Hall effects and various topological mechanisms in functionalized Sn monolayers

Yang

Zhou

et al. 2019

The topological behaviors of Sn monolayers partly passivated with H atoms are explored based on first-principles calculations. Obvious magnetism can be induced in the Sn monolayer due to the passivation. And the magnetism strength is found to be determined by the number difference of the H atoms bonding to the two sublattices of stanene. Quantum anomalous Hall (QAH) effects are found appearing easily in the systems with one of the sublattices fully passivated and the other not. The origin of the topological states can be ascribed to the coupling of the magnetism, the lattice symmetry (C 3v ), and the H-atom concentrations, which forms various mechanisms of the topological states. Particularly, band inversions are found playing completely different roles in forming the QAH effects for the different functionalized Sn monolayers.

“…Subsequently, the research on 2D TI with large gap became intensive. Many efforts have been made to find appropriate candidate compounds of large-gap 2D TI, such as Ge [7], Sn [8][9][10], Sb [11], and Bi [12]. Among them, bismuth has the strongest SOC strength along main group elements, and the Bi (111) bilayer, named bismuthene, is found to be a candidate 2D topological insulator supporting QSH effects, and has attracted a great deal of attention.…”

Section: Introductionmentioning

confidence: 99%

Giant gap quantum spin Hall effect and valley-polarized quantum anomalous Hall effect in cyanided bismuth bilayers

Chang-wen

Ding

et al. 2016

Bismuth (Bi) has attracted a great deal of attention for its strongest spin-orbit coupling (SOC) strength among main group elements. Although quantum anomalous Hall (QAH) state is predicted in halfhydrogenated Bi honeycomb monolayers Bi 2 H, the experimental results are still missing. Halogen atoms (X = F, Cl and Br) were also frequently used as modifications, but Bi 2 X films show a frustrating metallic character that masks the QAH effects. Here, first-principle calculations are performed to predict the full-cyanided bismuthene (Bi 2 (CN) 2 ) as 2D topological insulator supporting quantum spin Hall state with a record large gap up to 1.10 eV, and more importantly, half-cyanogen saturated bismuthene (Bi 2 (CN)) as a Chern insulator supporting a valley-polarized QAH state, with a Curie temperature to be 164 K, as well as a large gap reaching 0.348 eV which could be further tuned by biaxial strain and SOC strength. Our findings provide an appropriate and flexible material family candidate for spintronic and valleytronic devices.