Two-dimensional transition metal selenides M 2 Se : A platform for superconductivity, band topology, and charge density waves

MXenes and MBenes, which are two-dimensional (2D) transition metal carbides/nitrides and borides, have been extensively studied for their impressive properties. Recently, we reported a family of transition metal sulfides MSene (${M}_{2}\mathrm{S}$) with rich properties, it is worth studying whether selenides with similar structure also have rich properties. In this work, through high-throughput screening, we present a novel family of 2D transition metal selenides, ${M}_{2}\mathrm{Se}$. In this family, there are 58 candidate materials, of which 10 are stable and metallic. Notably, eight exhibit superconductivity, among which four are superconducting topological metals. Besides, 8 show charge density wave (CDW) behavior, among which 5 also exhibit antiferromagnetism. It is revealed that CDW originates from electron-phonon coupling rather than Fermi surface nesting. Moreover, strain can be applied to regulate the competition between the CDW and superconductivity. Our findings reveal the rich properties of superconductivity, band topology, CDWs, and magnetism in ${M}_{2}\mathrm{Se}$, providing a new platform for the controllable integration of multifunctional quantum states.