CDW

In spite of Coulomb repulsion some low-dimensional metallic systems spontaneously develop a static periodic modulation of the electron gas below a certain temperature. In one dimension this modulation, known as charge-density wave (CDW) and mostly understood as Peierls transition, can turn the metal into an insulator. In two dimensions (2D), in contrast, the resistivity below the transition can decrease with temperature even faster than in the normal phase. A basic prerequisite of the CDW in one dimension, the existence of favourable nesting conditions, could not be proven in 2D. In spite of a number of alternative theories, the mechanism of CDW in 2D remains unexplained. We study the mechanism of the charge-density waves formation in two dimensions and their possible relation to the superconductivity. The latest developments of the modern high-resolution angle-resolved photoemission spectroscopy is applied to investigate a series of transition-metal dichalcogenides which are well known representatives of the two-dimensional CDW-bearing compounds. Photoemission spectroscopy delivers the information about the size, shape, topology and the nesting properties of the Fermi surface; amplitude, anisotropy and character of the pseudo- and CDW energy gaps; dispersion of the electronic states, their symmetry and Fermi velocity; real and imaginary parts of the self-energy, charge susceptibility and a coupling strength to bosonic degrees of freedom. A significant improvement in the understanding of these correlated systems as well as the interrelation of CDW phenomenon and superconductivity is aimed.

ARPES Group