Structural evidence for Ta-tetramerization displacements in the charge-density-wave compound (TaSe4)2I from x-ray anomalous diffraction -: art. no. 015502

We use the anomalous x-ray diffraction technique to investigate the nature of the tantalum displacement pattern in the modulated phase of the charge-density-wave compound (TaSe4)(2)I. In addition to the known acousticlike modulation, we find the first direct evidence for the condensation of opticlike Ta displacements along the metallic chains corresponding to an LLSS pattern of long and short in-chain Ta-Ta distances (Ta-tetramerization modes). This result confirms a previous model in which the interaction of the electronically coupled optic modes with long-wavelength acoustic shear modes leads to the condensation of a modulation of mixed character.