Emergent superconductivity at 16.3 K in an altermagnetic candidate Na${}_{2-x}$V${}_2$Se${}_2$O with broken inversion symmetry

Abstract

Altermagnets (AMs), characterized by zero net magnetization and momentum-dependent spin splitting, are anticipated to hold significant potential for generating multiple exotic and uncommon superconducting states. However, superconductivity has not yet been realized in AMs to date. Recently, two-dimensional (2D) V${}_2$Ch${}_2$O (Ch = Se, Te) monolayers, as well as AV${}_2$Ch${}_2$O (A = K, Rb, Cs) crystals containing [V${}_2$Ch${}_2$O]${}^{\hat{I}´-}$ building layers, have been predicted and/or demonstrated to be promising altermagnetic materials. Our preliminary attempts to explore superconductivity in these materials by applying pressure or chemical doping were unsuccessful. Here we report the discovery of superconductivity at a relatively high transition temperature of ~ 16.3 K in a newly synthesized layered compound, Na${}_{2-x}$V${}_2$Se${}_2$O, a variant of AV${}_2$Ch${}_2$O. In this structure, the [V${}_2$Ch${}_2$O]${}^{\hat{I}´-}$ layers are interspersed with double layers of Na${}^{+}$ instead of a single layer of A${}^{+}$, with sodium sites being only half-filled. This new family of layered vanadium oxychalcogenides, lacking inversion symmetry, represents an intriguing platform for exploring altermagnetic superconductors, and holds the potential to reveal novel phenomena, such as topological states, van Hove singularities, and finite-momentum superconductivity. Furthermore, this material acts as a "bridge" between the cuprate/nickelate and iron-pnictide high temperature superconductors, providing new hope and opportunity to expand the category of layered superconductors with higher critical temperatures (T${}_c$) and enhancing our understanding of the underlying mechanisms in these systems.

31 pages, 5 figures