Topological Nodal Line Electrides: Realization of an Ideal Nodal Line State Nearly Immune from Spin-Orbit Coupling

Nodal line semimetals (NLSs) have attracted broad interest in current research. In most of the existing NLSs, the intrinsic properties of nodal lines are greatly destroyed because nodal lines usually suffer sizable gaps induced by non-negligible spin-orbit coupling (SOC). In this work, we propose the topological nodal line electrides (TNLEs), which achieve electronic structures of nodal lines and electrides simultaneously, and provide new insight into designing excellent NLSs nearly immune from SOC. Since the states near the Fermi level are mostly contributed by non-nucleus-bound interstitial electrons, nodal lines in TNLEs manifest an extremely small SOC-induced gap even possessing heavy elements. In particular, we propose that the family of A₂B (A = Ca, Sr, Ba; B = As, Sb, Bi) materials are realistic TNLEs with negligible SOC-induced gaps, which can act as excellent platforms to study the intrinsic properties of TNLEs.