Strong coupling charge-density waves in doped transition metal dichalcogenides

We present a theoretical study on a phase transition from quantum spin Hall insulating phase to strong coupling charge density wave (CDW) in adatom-doped single layer transition metal dichalcogenides (TMDs) 1T$'-M$Te$_2$ ($M$ = Mo and W) using first-principles calculation methods. It is shown that when 1T$'$ phase TMDs are doped by alkali metals or hydrogen atom, their Fermi surface shows quasi-one-dimensional features and phonon dispersion at the corresponding nesting vectors becomes unstable, turning 1T$'$ structure to diamond-shape (DS) chain phase with a substantial energy gap. The resulting CDW phase is compatible with a ground state of ReS$_2$ and ReSe$_2$. To unveil the origin of CDW phase transition, we calculate the electronic non-interacting susceptibility and electron-phonon coupling strength as a function of doping concentration and then find out that origin of phase transition is the strong electron-phonon coupling of the doped TMDs.