Unconventional superconductivity in $A$V$_2X_2$O family of surface altermagnets

Abstract

Motivated by the recent discovery of superconductivity at 16.3 K in layered oxychalcogenide Na$_{2-x}$V$_2$Se$_2$O we investigate pairing instabilities in the broader family of layered materials composed of V$_2$O planes, believed to exhibit altermagnetic order in their monolayer form. Even though the bulk family members KV$_2$Se$_2$O and Rb$_{1-δ}$V$_{2}$Te$_{2}$O are likely conventional antiferromagnets that show only surface altermagnetism, our analysis predicts exotic equal-spin triplet superconductivity as the dominant pairing instability in these materials. This is a consequence of their unique magnetic and sublattice structure that renders electron bands incompatible with conventional spin-singlet pairing. The predicted triplet superconducting phases are topologically non-trivial and capable of supporting spin-polarized persistent currents, properties potentially useful in technological applications.