Anti-Jahn-Teller effect induced ultrafast insulator to metal transition in perovskite BaBiO3

The Jahn-Teller (JT) effect involves the ions M with a degenerate electronic state distorting the corner-sharing MO6 octahedra to lift the degeneracy, inducing strong coupling of electrons to lattice, and mediating the exotic properties in perovskite oxides. Conversely, the anti-Jahn-Teller (AJT) effect refers to the deformation against the Jahn-Teller-distorted MO6 octahedra. However, it is difficult to experimentally execute both effects descending from the fine-tuning of crystal structures. We propose the AJT can be introduced by THz laser illumination at 11.71 THz in a candidate superconducting perovskite material BaBiO3 near room temperature. The illumination coherently drives the infrared-active phonon that excites the Raman breathing mode through the quadratic-linear nonlinear interaction. The process is characterized by the emergence of an AJT effect, accompanied by an insulator-to-metal transition occurring on the picosecond timescale. This study underlines the important role of crystal structure engineering by coherent phonon excitation in designing optoelectronic devices.