Electron-phonon driven charge density wave and superconductivity in a 1T−TaSi2N4 monolayer

Charge-density wave (CDW) and superconductivity, as well as their interplay, are fascinating topics in condensed-matter physics. In this work, we propose a single-layer (SL) CDW material, 1T-TaSi₂N₄, among synthesized two-dimensional (2D) MoSi₂N₄ family. Through first-principles simulations, its stability, vibrational properties, electronic structures, CDW, and superconductivity have been systematically scrutinized. The Ta-d_z² orbitals occupy mainly at the Fermi level and SL 1T-TaSi₂N₄ exhibits intrinsic metallic property. Besides, the CDW transition temperature (TCDW) is estimated to be ~500 K by using the temperature dependent effective potential technique. We found that it is the electron-phonon couping (EPC) that drives the CDW to form. Furthermore, its CDW orders can be manipulated by carrier doping and applying strain. At doping of 0.14 h/cell, the CDW instability is effectively suppressed and it changes to a 2D superconductor below ~21.84 K. Moreover, its superconducting transition temperature Tc under the strain of 10% is ~10.47 K. Physically, the superconductivity in stabilized 1T-TaSi₂N₄ monolayer is mainly contributed by the EPC between electrons from the Ta-d_z² orbitals and phonon vibrations from the Ta-xy and N-z modes with evident soft phonon mode.