High-pressure synthesis of fully sp2-hybridized polymeric nitrogen layer in potassium supernitride.

Searching for fully sp2-hybridized layered structures is of fundamental importance because of their fascinating physical properties and potential to host topologically non-trivial electronic states. However, the synthesis of fully sp2-hybridized layered polymeric nitrogen structures remains a challenging work because of their low stability. Here, we report the synthesis of a fully sp2-hybridized layered polymeric nitrogen structure featuring fused 18-membered rings in potassium supernitride (K2N16) under high-pressure and high-temperature conditions. Bader charge analysis reveals that the potassium atomic layer stabilizes the unique sp2-hybridized polymeric nitrogen layers through the charge transfer effect in K2N16. The calculation of electronic structure indicates that K2N16 is a topological semimetal with multiple Dirac points and hosts higher-order Dirac fermions with cubic dispersion, which are contributed by the sp2-hybridized polymeric nitrogen layers arranged in P6/mcc symmetry. The high-pressure synthesis of the fully sp2-hybridized polymeric nitrogen layered structure provides promising prospects for exploring novel topological materials with effective stabilization routes.