Engineering multifunctionality at oxide interfaces by multimode coupling

TL;DR

This study uses first-principles calculations to demonstrate how multimode coupling in oxide superlattices can control electronic and magnetic phases, enabling tunable insulator-metal-insulator transitions and polarization switching.

Contribution

It reveals a new mechanism of multimode coupling that enables control over multiple functionalities in oxide interfaces, expanding the design possibilities for multifunctional materials.

Findings

Identified a polar A-type charge disproportionation mode, Q_ACD.

Showed coupling between Q_ACD and Q_Tri modes influences symmetry and phases.

Demonstrated tunable phase transitions and polarization switching via mode coupling.

Abstract

We employed first-principles density functional theory calculations guided by group-theoretical analysis and demonstrated the control of insulator-metal-insulator transition, polarization and two sublattice magnetization in (LaFeO$_3$)$_1$/(CaFeO$_3$)$_1$ superlattice via. multi structural mode coupling i.e., 'multimode coupling'. We have discovered a polar A-type charge disproportionation mode, Q$_{ACD}$ (analogous to the A-type antiferromagnetic ordering), and found that it couples with the trilinear coupling, $Q_{Tri}$ mode (common in $Pnma$ perovskite oxides and involves three structural modes), and lowers the symmetry further. By tuning the strength of the coupling between the participating modes, the polar metallic phase, polar zero bandgap semiconducting, and polar insulating phases can be obtained. Here, $Q_{Tri}$ switches the polarization direction, whereas, Q$_{ACD}$ can trigger insulator-metal-insulator transition along with the polarization switching. The mechanism is true for any transition metal superlattices constituted with $Pnma$ building blocks and with partially filled $e_g$ or $t_{2g}$ electron(s) at the transition metal sites.