Doping induced charge density wave in monolayer TiS2 and phonon-mediated superconductivity

Abstract

Using the first-principles calculations, we have investigated the effects of the charge doping and biaxial strain on the charge density wave (CDW) of monolayer octahedral titanium disulfide (1T-TiS2). Our results show that proper electron doping can suppress the (2×2) CDW instability and the larger electron doping promotes a (7–√×3–√) CDW phase involving a spontaneous breaking of the hexagonal crystal symmetry. Strain can affect the stability of doped monolayer 1T-TiS2, but neither compressive strain nor tensile strain alone can stabilize the pristine one. When TiS2 layers are decorated by metal atoms, such as Li, Na, K, Ca, and Al, the transferred charge can also suppress the (2×2) CDW instability. The stable doped 1T-TiS2 is predicted to exhibit good phonon-mediated superconductivity, which can be further enhanced by strain. Our results reveal a unique CDW phenomenon in the electron-doped monolayer 1T-TiS2 and that doping combined strain is efficient to modulate phonon softening, electron-phonon coupling, and superconductivity.