RAPID COMMUNICATIONS PHYSICAL REVIEW B 94, 241403(R) (2016) Quantum spin Hall phase in stanene-derived overlayers on passivated SiC substrates Filipe Matusalem, 1 , * Friedhelm Bechstedt, 2 Marcelo Marques, 1 and Lara K. Teles 1 1 Grupo de Materiais Semicondutores e Nanotecnologia (GMSN), Instituto Tecnol´ ogico de Aeron´ autica (ITA), 12228-900 S ˜ ao Jos´ e dos Campos/SP, Brazil 2 Institut f ¨ ur Festk¨ orpertheorie und -optik, Friedrich-Schiller-Universit¨ at, Max-Wien-Platz 1, D-07743 Jena, Germany (Received 14 July 2016; revised manuscript received 29 September 2016; published 13 December 2016) We present atomic and electronic structure studies using first-principles calculations of two-dimensional topological insulators, stanene and fluorostanene, deposited on 4H -SiC(0001) substrates. We demonstrate the stability of H- or F-passivated honeycomb crystals due to a van der Waals interaction between the adsorbate and substrate. Despite destroyed inversion symmetry and biaxial strain the calculations of the band structures and Z 2 topological invariants predict that the quantum spin Hall (QSH) phase of stanene on H-passivated SiC as well as fluorostanene on H- and F-passivated SiC survives the interaction with the substrate. Our findings should serve as guidance for the epitaxial growth of tin-based QSH systems on wide-band-gap semiconductors. DOI: 10.1103/PhysRevB.94.241403 A new quantum state of matter that exhibits robust metallic boundary states inside the energy gap of the bulk, the topological insulators (TIs), has been discovered [1–4]. TIs are based on many crystals composed of heavy elements with a strong spin-orbit interaction (SOI). They have inspired in- creasing interest in physics, chemistry, and materials science to explore their promising potential for application in spintronics, thermoelectrics, and quantum computation [5]. TIs can be three-dimensional (3D) or two-dimensional (2D). The 2D case is most interesting because it represents the quantum spin Hall (QSH) phase [2,3] and is characterized by one topological invariant Z 2 [6]. The interior of such a 2D TI exhibits a spin-orbit gap, while topologically protected helical states are localized at its edges. Among the 2D materials, a promising TI candidate is stanene, a graphenelike monolayer of tin (Sn) atoms, resembling a buckled honeycomb lattice with relativistic Dirac fermions near the K point on the hexagonal Brillouin zone (BZ) [7,8]. At K a small gap of about 0.1 eV is opened by a SOI [9]. Stanene has been predicted to be a TI [7], while its counterpart, chemically functionalized with fluorine, has been identified as a QSH insulator with a large gap [8,10]. Moreover, it is suggested to be the wonder material of future electronics [11], predicted to conduct electricity with 100% efficiency at room temperature [8]. Stanene may also provide other interesting features such as enhanced thermoelectricity [12] and topological superconductivity [13]. Ground-state studies of freestanding 2D crystals are rather academic, in particular, for such which cannot be prepared by exfoliation. Their experimental investigations but especially their possible applications in electronic devices ask for their epitaxial growth on a certain substrate. Therefore, the search for substrates that preserve the TI character of the overlayer becomes essential for practical purposes. There have been trials to deposit Sn films on substrates. Pre- vious results of molecular beam epitaxy (MBE) experiments may be interpreted in terms of stanenelike overlayers [14]. Monolayer stanene has been recently fabricated by MBE on a Bi 2 Te 3 (111) substrate [15]. Its metallic properties have been * filipematus@gmail.com; gmsn@ita.br attributed to the strong interaction between Sn atoms and the substrate, illustrating the crucial role of the interaction with the substrate for maintaining the topological character. Despite the great importance of the substrate’s influence on the preservation of the intrinsic topology of 2D materials, only few works have investigated this fact [10,16,17]. There are some theoretical predictions of TI stanene on other 2D materials as substrates [18–20]. However, flakes of 2D crystals such as MoS 2 cannot serve as the substrate in a reliable epitaxy. Rather, commercial wafers of large-gap semiconductors may serve as a suitable substrate and open an avenue for future TI-based electronics. Recently, a triangular lattice of Sn atoms has been deposited on a SiC(0001) substrate [21]. This progress encourages further exploration of atomically thin Sn-based lattices on SiC. On the other hand, the passivation of SiC(0001) surfaces can play a fundamental role in obtaining a nonmagnetic wide-band-gap material free of surface states, possibly resulting in the survival of the TI character of the grown stanene-derived overlayers. Thus, a study in this direction could give important insights into the epitaxial growth achievement of such systems. In this Rapid Communication we investigate the deposition of stanene and fluorostanene on SiC, passivated or not with fluorine (F) or hydrogen (H), including the formation of quasifreestanding layers. Despite the wide gap of about 3 eV of the 4H -SiC polytype, the passivation of the substrate is mandatory for the survival of Dirac fermions. We develop first-principles electronic structure calculations to derive the topological Z 2 invariants of the adsorbate-substrate system without inversion symmetry. We predict that stanene on top of H-passivated and fluorostanene on top of H- and F-passivated 4H -SiC(0001) remain TIs. To study the deposition of tin-based 2D materials on SiC, we use state-of-the-art ab initio simulations based on the density functional theory (DFT) as implemented in the Vienna ab initio simulation package (VASP)[22]. The wave functions and potentials are generated within the projector-augmented wave method [23]. The exchange and correlation are computed using the generalized gradient approximation [24]. The van der Waals (vdW) interaction is taken into account in the framework of the optB86b functional [25–27]. The kinetic energy cutoff for the plane waves is restricted to 300 eV, and the BZ is 2469-9950/2016/94(24)/241403(5) 241403-1 ©2016 American Physical Society