Honeycomb lattice in metal-rich chalcogenide Fe2Te

Abstract

Two-dimensional honeycomb crystals have inspired intense research interest for their novel properties and great potential in electronics and optoelectronics. Here, through molecular beam epitaxy on SrTiO3(001), we report successful epitaxial growth of metal-rich chalcogenide Fe2Te, a honeycomb-structured film that has no direct bulk analogue, under Te-limited growth conditions. The structural morphology and electronic properties of Fe2Te are explored with scanning tunneling microscopy and angle resolved photoemission spectroscopy, which reveal electronic bands cross the Fermi level and nearly-flat bands. Moreover, we find a weak interfacial interaction between Fe2Te and the underlying substrates, paving a newly developed alternative avenue for honeycomb-based electronic devices. PACS: 81.15.Hi, 68.37.Ef, 68.55.−a, 74.70.Xa Introduction Following the advent of graphene, two-dimensional (2D) crystals with a honeycomb lattice have been at the forefront of materials of physics, thanks to their novel and potentially useful electronic structure . Specifically, the unique honeycomb lattice leads to Dirac-like bands where the charge carriers behave as massless particles . As 2D analogs of graphene, a few monoelemental Xenes, to wit, borophene , silicene , germanene , stanene, phosphorene , arsenene, antimonene, bismuthene, and tellurene, have been constantly synthesized and attracted worldwide attention for their unusual quantum spin hall effect, superconductivity and thermoelectric properties. Unlike graphene, however, most of these Xenes can only be stabilized as an adhesion layer on some specific substrates, seldom form a van der Waals layered bulk phase and readily develop as freestanding 2D sheets. Alternatively, honeycomb lattice compounds of two or more elements have been becoming increasingly popular as promising candidates for tunable Dirac cones. They, for example, include transition metal chalcogenides (TMCs) that commonly crystallize into the layered structure . As a representative TMC material, iron telluride exhibits multiple structural phases with distinct properties . For instance, the conventional phase of β-FeTe with a tetragonal PbOtype structure is an antiferromagnetic metal below around 70 K , whereas the hexagonal α-FeTe phase is ferromagnetic with the NiAs-type crystal structure . In addition, iron ditelluride FeTe2 is typically formed in nonlayered marcasite phase with an orthorhombic structure at ambient condition and considered as an antiferromagnetic semiconductor , although it becomes ferromagnetic at the 2D limit . As the electronic and magnetic properties of Fe-Te binary compounds are hypersensitive to minor change in stoichiometry and structure, phase-controlled preparation of them have been recently explored , primarily confined to the bulk stable phases. In this Letter, we have employed Te-limited growth conditions to epitaxially prepare a metal-rich telluride Fe2Te on SrTiO3(001) substrates. In situ scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) investigations reveal a honeycomb lattice of Fe2Te, featured by electron-like bands cross the Fermi level (EF) and extremely flat bands, which has no direct analogue to its bulk phase.