Charge-Density-Wave Transition in VSe₂ from First Principles

Among transition metal dichalcogenides (TMDs), VSe₂ is particularly interesting, as it develops a purely 3-dimensional (3D) charge-density wave (CDW) at T_CDW=110 K. High resolution inelastic x-ray (IXS) experiments have proved for the first time ever that the CDW transition in this compound is characterized by the collapse of an acoustic mode at the critical wave vector q_CDW=(2.25 0 0.7) r.l.u. and critical temperature T_CDW=110 K. This softening behaviour is ratified by our fully anharmonic ab initio calculations, which show that van der Waals interactions are crucial to melt the CDW. Our work also highlights the important role of out-of-plane interactions to describe 3D CDWs in TMDs. Finally, our first principles calculations determine a large momentum-dependence of the electron-phonon interaction in VSe₂, peaking at the CDW wavevector, in the presence of nesting.

Reference: arXiv:2007.08413 [cond-mat.mtrl-sci]