Cesium-involved electron transfer and electron-electron interaction in high-pressure metallic CsPbI₃

The rich electronic properties realized in perovskite oxides have motivated the search for novel electronic states in isostructural halide perovskites and related lattice architectures. By compressing δ-CsPbI₃ to 80 GPa, an insulator-to-metal transition occurs, concomitant with the completion of a sluggish structural transition from the one-dimensional (1D) Pnma (δ) phase to a 3D Pmn2₁ (ε) phase. Deviation from Fermi liquid (FL) behavior is observed in CsPbI₃ upon entering the metallic ε phase, which progressively evolves into a FL-like state at 186 GPa. First-principles density functional theory calculations reveal dramatically enhanced electron transfer and sudden increase of the 5d state occupation of Cs and I in the ε phase that strengthen the electron-electron interaction and render FL-like behavior. Our study presents a promising strategy for tuning the electronic interaction in halide perovskites for realizing intriguing electronic states.