Electron-phonon coupling in compressed 1T-TaS₂: Stability and superconductivity from first principles

The coexistence of charge-density waves and superconductivity in compressed 1T-TaS₂ is investigated through density-functional calculations. It has been speculated that this coexistence arises from a real-space phase separation of insulating domains of the commensurate-charge-density-wave phase and metallic interdomain regions. Approximating the structure of the interdomain regions with the undistorted 1T structure, the present calculations confirm that pressure suppresses the charge–density-wave instability and stabilizes the interdomain phase. The electron-phonon coupling constants of the compressed 1T phase are found to have strong wave-vector dependence, with large contributions from soft modes associated with the incipient charge-density wave instability. The pressure dependence of the coupling parameters is discussed in relation to the measured insensitivity of the superconducting transition temperature to pressure.