Origin of ferroelectricity and superconductivity with nontrivial electronic topology in fluorinated Nb2N

Two-dimensional (2D) intrinsic superconductors with nontrivial topological band and vertical ferroelectricity exhibit fascinating characteristics for achieving electrostatic control of quantum phases. Only a few such 2D materials have been theoretically predicted. In this paper, based on first-principles calculations, we explore the superconductivity and ferroelectric properties in fluorinated 2D ${\mathrm{Nb}}_{2}\mathrm{N}$. In the stable ${\mathrm{Nb}}_{2}{\mathrm{NF}}_{2}, {H}_{3}\text{\ensuremath{-}}{\mathrm{Nb}}_{2}{\mathrm{NF}}_{2}$ breaks the spatial inversion symmetry, exhibiting vertical ferroelectric. More interestingly, it not only possesses intrinsic superconductivity with superconducting transition temperatures (${T}_{c}$) of 10 K, but also exhibits nontrivial band topology. ${H}_{1}\text{\ensuremath{-}}{\mathrm{Nb}}_{2}{\mathrm{NF}}_{2}$ shows topological band and superconductivity with ${T}_{c}$ of 32 K, surpassing most of the 2D conventional topological superconductors' candidates. Our research has enriched 2D superconducting materials with nontrivial band topology and ferroelectric properties, and provided a theoretical basis for the preparation of devices switching between superconducting and ferroelectric states with external electric field.