Interplay between structure and electronic properties of layered transition-metal dichalcogenides: Comparing the loss function of1Tand2Hpolymorphs

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 − 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.

Valley plasmonics in transition metal dichalcogenides

“…On the one side there are models combining effective k · p descriptions of the quadratic electronic bands around the band gap with an evaluation of the dielectric function within the random phase approximation 29,30 . On the other side, there are RPA descriptions based on full density functional theory calculations, which include realistic single particle band structures describing the complete Brillouin zone 32,[38][39][40][41][42] . Here, we add a third approach by utilizing a materialspecific low-energy model Hamiltonian derived from ab initio calculations for the undoped material as the basis for the evaluation of dynamical response functions in the electron and hole doped situations.…”

Negative plasmon dispersion in 2H-NbS2beyond the charge-density-wave interpretation

“…Even alkali metals [13][14][15][16][17][18][19][20] have been shown to exhibit several deviations from the jellium model including negative plasmon dispersion. Starting from this observation, a different interpretation of the negative plasmon dispersion in 2H-TMDs has been given on the basis of first principle calculations [21][22][23]. As shown in [22], the unusual dispersion in this class of materials is due to the peculiar behavior of intraband transitions that contribute to the plasmon excitation.…”

Dynamical screening in SrVO3 : Inelastic x-ray scattering experiments and ab initio calculations

“…3(b can conclude that LFEs are the key for the coupling between independent electron-hole excitations at large q and the first-Brillouin-zone plasmon. This effect is well known in layered materials [76][77][78][79][80][81][82][83][84][85], which are intrinsically inhomogeneous in the direction perpendicular to the layers, and where LFEs give rise to a long-lived plasmon that continues to exist well beyond the first Brillouin zone. In these situations, the mechanism behind the reappearance of the first-Brillouin-zone q r spectra at larger momentum transfers q r + G can be understood within a two-plasmon-band model [80,86].…”