First-principles study of superconductivity in the two- and three-dimensional forms of PbTiSe2 : Suppressed charge density wave in 1T−TiSe2

Abstract

Layered $1T\text{\ensuremath{-}}{\mathrm{TiSe}}_{2}$ has attracted much interest for the competition of charge density wave (CDW) and superconductivity in its bulk and even monolayer forms. Here we perform first-principles calculations of the electronic structure, phonon dispersion, and electron-phonon coupling of the Pb-intercalated $1T\text{\ensuremath{-}}{\mathrm{TiSe}}_{2}$ in bulk and layered structures. Results show that upon the Pb atom intercalation, the CDW instability in $1T\text{\ensuremath{-}}{\mathrm{TiSe}}_{2}$ can be effectively suppressed, accompanied by the removal of the imaginary phonon modes at q${}_{\mathrm{M}}$. The Pb $6p$ orbitals occupy directly at the Fermi level. Both bulk and layered ${\mathrm{PbTiSe}}_{2}$ are phonon-mediated superconductors, with estimated superconducting temperature ${T}_{c}$ to be $\ensuremath{\sim}1.6$--3.8 K. The main contribution to the electron-phonon coupling is from the vibrations of Pb and Se atoms and the superconductivity is mainly raised by Pb. The superconducting related physical quantities are found tunable by varying Pb content.