Cesium-mediated electron redistribution and electron-electron interaction in high-pressure metallic CsPbI3.

Electron-phonon coupling was believed to govern the carrier transport in halide perovskites and related phases. Here we demonstrate that electron-electron interaction enhanced by Cs-involved electron redistribution plays a direct and prominent role in the low-temperature electrical transport of compressed CsPbI₃ and renders Fermi liquid (FL)-like behavior. By compressing δ-CsPbI₃ to 80 GPa, an insulator-semimetal-metal transition occurs, concomitant with the completion of a slow structural transition from the one-dimensional Pnma (δ) phase to a three-dimensional Pmn2₁ (ε) phase. Deviation from FL behavior is observed upon CsPbI₃ entering the metallic ε phase, which progressively evolves into a FL-like state at 186 GPa. First-principles density functional theory calculations reveal that the enhanced electron-electron coupling results from the sudden increase of the 5d state occupation in Cs and I atoms. Our study presents a promising strategy of cationic manipulation for tuning the electronic structure and carrier scattering of halide perovskites at high pressure. Halide perovskites display physical properties that are of both practical and fundamental interest. At high pressure, the low-temperature electrical transport in one such compound, CsPbI₃, is now shown to be due to Cs-mediated electron-electron interactions resulting in Fermi-liquid-like behaviour. [ABSTRACT FROM AUTHOR]