Speaker
Description
Rare-earth nickelates, RNiO$_{3}$, are negative charge-transfer materials with electronic configuration of Ni-3$d^8\underline{L}$ ($\underline{L}$ = oxygen ligand hole) in their metallic state. Most RNiO$_{3}$ undergo low-temperature metal-to-insulator transition (MIT) accompanied by breathing distortion in their crystal structure, where neighboring expanded NiO$_{6}$ octahedra (Ni-3$d^8$ configuration) alternate with collapsed NiO$_{6}$ (Ni-3$d^8\underline{L}^{2}$). Here, using resonant inelastic x-ray scattering, we reveal that the electron-phonon coupling (EPC) of the breathing-mode phonon significantly increases as NdNiO$_{3}$ undergoes MIT. Meanwhile, no significant changes are observed in the EPC of LaNiO$_{3}$ (SmNiO$_{3}$), which stays metallic (insulating) at all studied temperatures. These results confirm the major role that the breathing distortion and its EPC play in the MIT of RNiO$_{3}$.
