The role of charge density waves in structural transformations of 1T TaS2

Abstract

Electron and X-ray diffraction studies have identified three metastable phases in 1T TaS₂. Extra reflexions are interpreted as arising from charge density waves coupled to periodic distortions modulating a trigonal lattice. These waves are incommensurate with the matrix in 1T₁ and 1T₂, but form a commensurate super-lattice in 1T₃. Within 1T₂, the temperature dependence of the wave vector is correlated with a change in the cross-section of the Fermi surface, while the diffuse scattering which accompanies the discrete reflexions in 1T₁ is discussed as an image of this surface in the phonon spectrum. Changes in the stacking of distortions and in their amplitude are also reported.