Electronic Structure of the Metastable Epitaxial Rock-Salt SnSe {111} Topological Crystalline Insulator

Abstract

Topological crystalline insulators have been recently predicted and observed in rock-salt structure SnSe f111g thin films. Previous studies have suggested that the Se-terminated surface of this thin film with hydrogen passivation has a reduced surface energy and is thus a preferred configuration. In this paper, synchrotron-based angle-resolved photoemission spectroscopy, along with density functional theory calculations, is used to demonstrate that a rock-salt SnSe f111g thin film epitaxially grown on Bi 2 Se 3 has a stable Sn-terminated surface. These observations are supported by low-energy electron diffraction (LEED) intensity-voltage measurements and dynamical LEED calculations, which further show that the Sn-terminated SnSe f111g thin film has undergone a surface structural relaxation of the interlayer spacing between the Sn and Se atomic planes. In sharp contrast to the Se-terminated counterpart, the observed Dirac surface state in the Sn-terminated SnSe f111g thin film is shown to yield a high Fermi velocity, 0.50 × 10 6 m=s, which suggests a potential mechanism of engineering the Dirac surface state of topological materials by tuning the surface configuration.

The 2019 materials by design roadmap

“…Similarly, metastable rock-salt structure in SnSe thin film in Fig. 2(b) can be stabilized by depositing it epitaxially on a suitable substrate [6].…”

“…GaAs shell suppresses GaAsSb phase segregation, while the alloy without shell decomposes into GaSb-rich (red) and GaAs-rich (light blue) alternating segments. [5]; (b) crystal structure of topological insulator SnSe in its metastable rock-salt structure, stabilized by low-temperature molecular beam epitaxy on GaAs substrate [6]. (c) (top) The energies of the growing nuclei versus the number of atoms, E(n), show how the substrate steers the synthesis from the 3D towards 2D route by suppressing the nucleation barrier; (bottom) computed charge density shows how the Ag substrate donates electrons (from pink to blue) to the boron layer to stabilize its 2D structure [10].…”

Phase transition and electronic structure evolution of MoTe2 induced by W substitution

“…Note that multiple locations were surveyed across the sample surface, and no phase coexistence was observed. In addition, to examine any major changes in crystal structure within surface layers, the surface structure of these Mo 1x W x Te 2 alloys was determined using dynamical LEED calculations [38][39][40]. The optimized surface structure for 2H -and T d phase were obtained by fitting the calculated I-V curves to the measured ones.…”

Spectroscopic photoemission and low-energy electron microscopy studies of the surface and electronic structure of two-dimensional materials

“…However, due to advances in MBE growth techniques, preparation of the metastable SnSe f111g surface has now been successfully realized [111]. LEED I-V analysis is a powerful tool to explore the surface termination of SnSe thin films and reveal mechanisms for stabilizing a polar surface [112]. Figure 7 shows the calculated I-V curves of an optimized SnSe f111g surface structure.…”

“…Calculated LEED I-V curves of the (00) diffraction beam for an optimized Snterminated surface (green solid curve) and a Se-terminated surface (blue solid curve) and the measured I-V curve (red dots). Reproduced with permission from Ref [112].…”