Large spin splitting and strain-tunable valley physics in two-dimensional oxide BaO.

Two-dimensional (2D) oxide valleytronic materials are an emerging class of low-dimensional functional materials. However, high-performance oxide-based valleytronic candidates remain far less explored compared with their mature transition metal chalcogenide (TMD) counterparts. Based on density functional theory calculations, we systematically investigate the structural stability, electronic and spin properties, optical responses, and strain tunability of monolayer BaO exfoliated from the bulk BaO (111) surface. Our calculated results show that monolayer BaO exhibits robust dynamical, thermal, and mechanical stability, a sizable indirect band gap of 2.14 eV, and prominent spin splitting at the K (K') valleys. Furthermore, its band gap and the magnitude of spin splitting can be effectively modulated by external strain. Benefiting from its excellent structural stability, remarkable valley spin splitting, and flexible strain tunability, monolayer BaO is demonstrated to be a promising 2D oxide valleytronic material. This work provides a new alternative candidate for the design and development of high-performance spintronic and valleytronic nanodevices.