Superconductivity of VSe2 under pressure and charge doping: Suppressed charge density wave

By employing the first-principles calculations, the influence mechanism of external pressure and charge doping on the electron-phonon coupling (EPC) and superconductivity (SC) of bulk VSe₂ is investigated. Our calculations reveal that with increasing pressure the charge density wave (CDW) of 1T-VSe₂ is gradually suppressed, and a SC state subsequently emerges which is accompanied by a structural phase transition from the trigonal phase to a monoclinic phase at 15.50.28em0exGPa. Increasing pressure from 15.5 to 350.28em0exGPa, the SC transition temperature Tc of VSe₂ slightly increases from 4.2 to 5.20.28em0exK and no SC dome is found, which are in good agreement with the previous experimental results [S. Sahoo et al., Phys. Rev. B 101, 014514 (2020)]. Through electron- or hole-doping (denoted by nₑ and nₕ), the CDW order of the trigonal phase can be suppressed and SC states with Tc greater than 10.5 and 9.00.28em0exK, respectively, emerge. The highest Tc under charge doping can be up to about 120.28em0exK, and a weak double-dome like dependence of Tc on nₑ and nₕ is found. Combining systematical analysis of effects of pressure and charge doping, we demonstrate that the Kohn anomalies of phonons at certain Q points associated with the in-plane vibrations of V atoms play key roles in strengthening the EPC, which brings about the intriguing SC in VSe₂. However, due to the weak pressure-induced modifications of phonon spectrum as well as Fermi surface (FS), the changes of EPC and Tc caused by pressure are not significant. Interestingly, charge doping will produce a local flat band along ΓA direction near the FS, which is mainly contributed by V $3d$-orbitals, and result in large values of electronic density of states at Fermi level. Therefore, the effects caused by charge doping to the electronic structures, phonon anomalies, EPC, and Tc are evident. Our findings may provide a promising understanding to the pressure and doping-dependent SC of VSe₂, and may be valuable for designing new materials with enhanced SC through the strategic manipulation of electronic and phononic properties.