Effect of dimensionality and spin-orbit coupling on charge-density-wave transition in 2H-TaSe2

A first-principles investigation of the charge-density-wave (CDW) instability in bulk and single-layer 2H-TaSe2 is presented, focusing on the origin of the CDW instability, the role of the interlayer interactions, and the effect of spin-orbit coupling. While interlayer interactions and spin-orbit coupling have a nontrivial effect on the electronic structure and Fermi surface, the CDW instability is predicted to remain robust, with little or no change in the ordering wave vector. This is in contrast to the closely related 2H-NbSe2 material, where the CDW wave vector depends on dimensionality. The results are analyzed in terms of the interplay between the momentum dependence of the electron-phonon coupling and that of the electronic response function.