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 physics.
• Previous models often simplified the interactions or degrees of freedom involved.

Purpose of the Study:

• To develop a comprehensive three-dimensional multi-orbital tight-binding model for rare-earth nickelates.
• To investigate the competing insulating phases and their underlying mechanisms.
• To explore the role of electron-phonon and Jahn-Teller couplings in RNiO electronic behavior.

Main Methods:

• Developed a 3D multi-orbital tight-binding model.
• Extracted model parameters from hybrid-functional density functional theory (DFT) calculations for LuNiO.
• Analyzed the interplay of on-site interactions, electron-phonon coupling, and Jahn-Teller distortions.

Main Results:

• Identified three competing insulating phases governed by electron-phonon and Jahn-Teller couplings.
• Found that large on-site interactions stabilize insulating states via local Jahn-Teller distortions.
• Observed charge disproportionation leading to a spin-polarized charge-ordered state for smaller on-site interactions.
• Predicted a novel metastable charge- and orbital-ordered insulating phase driven by Jahn-Teller energy exceeding Hund's exchange, existing even without magnetic order.

Conclusions:

• The proposed model accurately captures the complex electronic phases in rare-earth nickelates.
• Jahn-Teller distortions play a critical role in stabilizing insulating states, with or without magnetic order.
• A nonmagnetic, charge-ordered insulating phase with Jahn-Teller distortions is predicted as a metastable state, challenging the necessity of magnetic order for metal-insulator transitions in RNiO.