Abstract
Transition-metal dichalcogenides (TMD) share the same global layered structure, but distinct polymorphs are characterized by different local coordinations of the transition-metal atoms. Here we compared the $1T$ and $2H$ families of metallic TMD, both in the bulk and in the two-dimensional forms. By means of first-principles time-dependent density functional calculations of the loss function, we established the direct connection between the low-energy plasmon properties and the crystal-structure symmetry. The different atomic environments affect the $d\ensuremath{-}d$ electron-hole excitations, which are prominent at low energies, resulting in distinct in-plane plasmon dispersions in the two families. Conversely, the different periodicity of the plasmon reappearance along the $c$ axis perpendicular to the layers can be used to distinguish the various crystal structures of TMD.
Highlights
Layered materials in which quasi-two-dimensional sheets are taken together by weak van der Waals interactions are ideal to synthesize low-dimensional systems such as one-dimensional (1D) nanotubes and two-dimensional (2D) nanosheets [1,2,3]
Since the different Transition-metal dichalcogenides (TMD) polymorphs are basically distinguished by the different stacking along the c axis, one would expect that the in-plane physics should be very similar for all of them
By comparing the loss functions and the plasmon dispersions of two different families of transition-metal dichalcogenides, we have established a detailed connection between the crystal structure and the electronic properties of these materials
Summary
Layered materials in which quasi-two-dimensional sheets are taken together by weak van der Waals interactions are ideal to synthesize low-dimensional systems such as one-dimensional (1D) nanotubes and two-dimensional (2D) nanosheets [1,2,3]. The lack of a band gap in the electronic band structure of graphene makes its application in electronics and optoelectronics difficult [5,6] This has stimulated the research into alternative classes of layered materials with more versatile electronic properties. The synthesis of isolated sheets of TMDs allows one to obtain 2D systems characterized by both metallic and insulating behavior [13]. Through a detailed comparative analysis of the low-energy spectra where d − d electron-hole excitations are prominent, we show how the loss function is a powerful tool to identify the fingerprints of the connection between the different crystal structures and the electronic properties of these layered materials
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