Non-magnetic insulating phase induced by Jahn-Teller effect in RNiO₃

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Rare-earth nickelates (RNiO) exhibit complex electronic properties, including metal-insulator transitions.
• Understanding the interplay of charge, spin, orbital, and lattice degrees of freedom is crucial for RNiO.
• Existing models often struggle to capture the full complexity of these materials.

Purpose of the Study:

• To develop a comprehensive three-dimensional multi-orbital tight-binding model for RNiO.
• To investigate the competing insulating phases and their underlying mechanisms.
• To explore novel electronic states and their stability.

Main Methods:

• Developed a 3D multi-orbital tight-binding model.
• Extracted model parameters from hybrid-functional density functional theory (DFT) calculations.
• Investigated electron-phonon (el-ph) coupling to breathing and Jahn-Teller (JT) modes.

Main Results:

• The model describes three competing insulating phases.
• Phase stability is governed by Hund's exchange and el-ph coupling.
• Charge disproportionation leads to a spin-polarized charge-ordered state for smaller interactions.
• A novel metastable charge- and orbital-ordered insulating phase emerges when JT energy exceeds Hund's exchange.

Conclusions:

• The interplay of interactions and lattice distortions dictates RNiO insulating phases.
• A nonmagnetic, charge-ordered insulating phase with JT distortions is predicted.
• Magnetic order is not a prerequisite for metal-insulator transitions in RNiO.