Competition between Ta-Ta and Te-Te bonding leading to the commensurate charge density wave in TaTe4

Abstract

The origin of the charge density wave in TaTe 4 is discussed on the basis of a first-principles density functional theory analysis of the Fermi surface, electron-hole response function, phonon band structure of the average structure, and structural optimization of the modulated phase. Analysis of the band structure and Fermi surface of the average structure clearly proves that despite the presence of TaTe 4 chains in the crystal structure, TaTe 4 is in fact a 3D material as far as the electronic structure near the Fermi level is concerned. A Fermi surface nesting mechanism is dismissed as the origin of the 2a × 2a × 3c structural modulation. The optimized 2a × 2a × 3c structure, which is found to be the more stable modulation in agreement with the experimental observations, can be obtained directly from a soft-phonon mode computed for the undistorted structure. Our results suggest that the driving force for the distortion is the maximization of Ta-Ta metal-metal bonding subject to inducing the minimum bonding decrease in the Te sublattice.

Structural approach to charge density waves in low-dimensional systems: electronic instability and chemical bonding

“…Finally note that an enhanced inter-chain coupling kills the 1D electronic divergence, as recently found in the calculation of the Lindhard response for TaTe 4 [219,220], a metallic system exhibiting a 2 × 2 × 3 CDW modulation [221] (see section 8.3). Although this solid is usually described as a tetragonal array of TaTe 4 chains, thus suggesting a pseudo-1D electronic structure, a careful analysis of the structure shows that the chains (along the c-direction) are tightly interconnected through Te … Te interactions.…”

“…Two DFT studies of the CDW in TaTe 4 have been recently reported [219,220] providing clear evidence for a strong coupling scenario of the CDW. Guster et al [219] have shown that there is a strong overlap between the Ta 5d z2 and Te p bands leading to a FS that contains both strongly warped pseudo-1D and 3D components.…”

“…Two DFT studies of the CDW in TaTe 4 have been recently reported [219,220] providing clear evidence for a strong coupling scenario of the CDW. Guster et al [219] have shown that there is a strong overlap between the Ta 5d z2 and Te p bands leading to a FS that contains both strongly warped pseudo-1D and 3D components. The electron-hole response does not contain any peak for the wave vector associated with the experimentally observed modulation [219] so that a FS driven mechanism can be dismissed.…”

“…In contrast, VS 4 , which also contains an array of VS 4 chains where V is in a square antiprismatic coordination as Ta in TaTe 4 and contains the same number of valence electrons, undergoes a standard Peierls instability doubling the periodicity along the chains. The reason is that the inter-chain S … S contacts in VS 4 are weak and the solid can be legitimately considered as 1D [219].…”

“…Guster et al [219] have shown that there is a strong overlap between the Ta 5d z2 and Te p bands leading to a FS that contains both strongly warped pseudo-1D and 3D components. The electron-hole response does not contain any peak for the wave vector associated with the experimentally observed modulation [219] so that a FS driven mechanism can be dismissed. The strong overlap between the Ta 5d z2 and Te p bands is at the origin of a filling of the Ta 5d z2 band quite different from the half-filling situation expected for the case with well-separated bands.…”