First-principles investigation of the charge-density-wave instability in1T-TaSe2

Abstract

The charge-density-wave (CDW) instability in $1T{\text{-TaSe}}_{2}$ is investigated as a function of pressure. Density-functional calculations accurately capture the instability at ambient pressures and predict the suppression of the CDW distortion under pressure. The instability is shown to be driven by softening of selected phonon modes due to enhanced electron-phonon matrix elements, rather than by nesting of the Fermi surface or other electronic mechanisms. In addition, the electronic structure of $1T{\text{-TaSe}}_{2}$ and $1T{\text{-TaS}}_{2}$ are compared to investigate why the electronic transition that accompanies the structural transition in the sulfide is not observed in the selenide. Finally, the possibility of electron-phonon superconductivity in compressed ${\text{TaSe}}_{2}$ is discussed.