Discovery of twin orbital-order phases in ferromagnetic semiconducting VI3 monolayer

Abstract

Spontaneous orbital symmetry breaking in crystals gives rise to abundant novel and interesting physical properties, which sometimes are concealed by the absence of geometrical distortions. We show that a recently discovered 3d² system, namely the layered VI₃ ferromagnetic semiconductor, is a strongly correlated and orbital ordering system. Our analysis reveals that in a VI₃-like system, there could be two types of orbital splitting, which are stabilized respectively by strong electronic correlation and inter-atomic exchange interactions. Consequently, on the basis of first-principles calculations, two competing low-energy phases of VI₃ monolayer (denoted as twin orbital-order phases) are discovered, in which the metal–insulator transition is driven by strong electronic correlation, and the orbital symmetry breaking is robust against geometrical distortions. In addition, similar phenomena are also observed in other VI₃-like systems. These findings shed light on the unusual electronic behavior of a strongly correlated 2D system and will be interesting for nanoscale multi-functional spintronic applications.