Square Nets of Tellurium:  Rare-Earth Dependent Variation in the Charge-Density Wave of RETe₃ (RE = Rare-Earth Element)

Abstract

The distortions in the square tellurium nets long known to exist in the structures of the charge-density wave materials, RETe3, have been elucidated. The (Te2)1- nets contain polytelluride oligomers which propagate in a fashion incommensurate from the adjacent (RETe)+ sublattice. The new information sets the stage for a much deeper understanding of these systems.

Effect of chemical pressure on the charge density wave transition in rare-earth tritelluridesRTe3

“…For most of the rare earths, the material has an incommensurate lattice modulation at room temperature, with a single in-plane wave-vector of approximately 2/7 c * (c * = 2π/c). 5,6,7,8,9 For the heaviest rare earths, the same modulation has been observed slightly below room temperature. 10 The band structure has been calculated for the unmodulated structure, yielding a simple FS consisting of slightly warped inner and outer diamond sheets formed from p x and p z orbitals of Te atoms in the square planar layers, both doubled due to the effects of bilayer splitting, with minimal baxis dispersion.…”

“…The Te-Te bond-length in RTe 3 is substantially longer than the standard covalent bond-length, implying that the unmodulated high-temperature structure of RTe 3 is inherently unstable, regardless of the lowdimensional electronic structure. 6 The close correspondence between the maxima in χ(q) and the observed superlattice wave vectors clearly demonstrates that the electronic system plays a preeminent role in the lattice modulation in this material. But it is not clear whether it is the only driving force for the instability.…”

Structural dynamics of two-dimensional charge-density waves in CeTe3investigated by ultrafast electron crystallography

“…The CeTe 3 [21][22][23][24] layered compound has a unit cell composed of a metallic planar net of Te sandwiched by the insulating corrugated double layers of CeTe [21,24], as depicted in Fig. 1a.…”

“…1a. The charge density waves reside within the 2D square Te net and cause a uniaxial periodic lattice distortion at wave vector Q 0 =0.28c*, which can be characterized by transmissive diffraction as satellites [21,24,25] distributed on the sides of main Bragg reflections, indexed as (m,n) based on reciprocal wave vector q=ma*+nc*. Unlike 1T-TaS 2 , the unidirectional p-wave CDW in CeTe 3 breaks the underlying square lattice symmetry and has a weak electron correlation, which present some unique advantages in de-convoluting the CDW-specific structural effects from the uncorrelated 2D lattice dynamics following optical quenching.…”

“…The lattice constant a=4.384Å, b=26.05Å, c=4.403Å [21]. The femtosecond (fs) electron pulse is directed along b-axis, producing a transmission diffraction pattern.…”