1D cuprates ACuO2 (A=Li, Na, K, Ru, Cs): not a simple atomic insulator

Abstract

Insulators are generally categorized into topological nontrivial and trivial one based on the presence and absence of topological invariant. While topological nontrivial insulators have attracted significant attention, advancements in classifying trivial insulators remain restricted. Recently, a class of unconventional atomic insulators, termed Berry obstructed atomic insulators (BOAIs), has emerged. The unconventionality is not captured by any symmetry eigenvalue, but identified by the mismatch between Wannier charge centers (WCCs) and the atomic positions. In this work, we connect the charge state of insulators with the unconventionality. Firstly, we present a tight-binding (TB) model to demonstrate how strong co-valency naturally endows BOAIs. As a negative charge-transfer energy insulator, one-dimensional (1D) cuprates ACuO2 (A = Li, Na, K, Ru, Cs) exhibit strong co-valency feature. It is demonstrated that ACuO2 are not simple atomic insulators, but qualified as BOAIs. The unconventionality is verified by both topological quantum chemistry analysis, first-principles calculations, and the obstructed surface states simulation. Our work not only enriches the family of BOAIs, but also bridges charge states of insulators and unconventional phases, which will arouse broad interest from both material and chemical communities.