Topological Electride Phase of Sodium at High Pressures and Temperatures

Abstract

Ab initio evolutionary structure searches coupled with quasiharmonic calculations predict that the insulating Na hP 4 phase transitions to a novel P 63/m phase between 200 GPa at 150 K, and 350 GPa at 1900 K. P 63/m Na is a topological semimetal with a Dirac nodal surface that is protected by a non-symmorphic symmetry, S2z. It is characterized by localized non-nuclear charge within 1D honeycomb channels and 0D cages rendering it an electride. These results highlight the complexity of warm dense sodium's electronic structure and free energy landscape that emerges at conditions where ionic cores overlap.