Ferromagnetism, Jahn-Teller effect, and orbital order in the two-dimensional monolayer perovskite Rb2CuCl4

Two-dimensional (2D) ferromagnetic (FM) semiconductors have attracted increasing interest for advanced spintronics. Here, we report that the monolayer perovskite Rb₂CuCl₄ (RCC) exhibits an intrinsic 2D FM semiconductor feature, emergent Jahn-Teller (JT) effect, and related orbital order (OO) with the diversity and tunability of physical behaviors. First-principles calculations and Monte Carlo simulations reveal the crucial changes of OO type, related mechanism of ferromagnetism, and electronic structure during the transition of JT distortion. Finally, we examine the significant tunable effect of biaxial strain on electronic and magnetic properties. Our comprehensive work on magnetism, structural distortion, and the electronic properties of monolayer RCC provides a guideline for studying the physical phenomena of 3 d⁹ Cu(II) in 2D halide perovskites.