Designing 3D topological insulators by 2D-Xene (X = Ge, Sn) sheet functionalization in GaGeTe-type structures

Abstract

State-of-the-art theoretical studies anticipate a 2D Dirac system in the ''heavy'' analogues of graphene, free-standing buckled honeycomb-like Xenes (X = Si, Ge, Sn, Pb, etc.). Herewith we regard a 2D sheet, which structurally and electronically resembles Xenes, in a 3D periodic, rhombohedral structure of layered AXTe (A = Ga, In; X = Ge, Sn) bulk materials. This structural family is predicted to host a 3D strong topological insulator with Z 2 = 1;(111) as a result of functionalization of the Xene derivative by covalent interactions. The parent structure GaGeTe is a long-known bulk semiconductor; the ''heavy'', isostructural analogues InSnTe and GaSnTe are predicted to be dynamically stable. Spin-orbit interaction in InSnTe opens a small topological band gap with inverted gap edges that are mainly composed of the In-5s and Te-5p states. Our simulations classify GaSnTe as a semimetal with topological properties, whereas the verdict for GaGeTe is not conclusive and urges further experimental verification. The AXTe family structures can be regarded as stacks of 2D layered cut-outs from a zincblende-type lattice and are composed of elements that are broadly used in modern semiconductor devices; hence they represent an accessible, attractive alternative for applications in spintronics. The layered nature of AXTe should facilitate the exfoliation of their hextuple layers and manufacture of heterostructures.

Possible experimental realization of a basic Z2 topological semimetal in GaGeTe

“…One can also notice that the experiment has more spectral weight at particular k z values, although an admixture from other k z 's is still visible. This observation agrees well with the moderate k z -resolution concluded from the Fermi surface map shown in panel c. Within the considered energy range, we note a good agreement between experiment and theory, independent of which exchange-correlation functional, PBE or HSE, is used to describe the occupied electronic structure of GaGeTe [10]. Now we can address its k z dependence in more details by comparing the data collected with differing photon energies.…”

“…3c,d). According to DFT calculations, in the case of the HSE functional, the band structure is topologically trivial with a rather large direct gap (550 meV) with the gap extrema located exactly in the T -point of 3D BZ [10]. In the case of the PBE functional, the band gap size is smaller (30 meV) and the gap is indirect, implying the topological character of the electronic spectrum.…”

“…The layered compound GaGeTe was first synthesized and structurally characterized quite long ago [5,6], and its phonon structure [7], thermoelectric [8] and transport [9] properties were consequently studied. However, the first theoretical study of its bulk electronic structure has appeared very recently [10] and has sparked strong interest in the surface electronic structure of this material [11]. In [10] structural and electronic resemblance between a structure fragment of the layered GaGeTe bulk and a heavy analogue of graphene, germanene [12], has been highlighted.…”

“…However, the first theoretical study of its bulk electronic structure has appeared very recently [10] and has sparked strong interest in the surface electronic structure of this material [11]. In [10] structural and electronic resemblance between a structure fragment of the layered GaGeTe bulk and a heavy analogue of graphene, germanene [12], has been highlighted. 2D materials with buckled honeycomb atomic arrangements, e.g.…”

“…First-principle calculations per-arXiv:1812.01668v1 [cond-mat.mtrl-sci] 4 Dec 2018 formed by co-authors in Ref. [10] have shown a possibility of a topological band inversion in its electronic spectrum driven by spin-orbit coupling. The valence and the conduction bands invert at the T -point, opening up a narrow indirect gap of the order of 30 meV.…”