Quantum Geometric Origin of Strain-Induced Ferroelectric Phase Transitions.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Ferroelectric (FE) materials are crucial for various applications.
• Existing theories like soft-phonon and Jahn-Teller effect offer phenomenological understanding.
• Microscopic strain-regulation mechanisms in FE materials remain unclear.

Purpose of the Study:

• To elucidate the microscopic connection between strain regulation and ferroelectricity.
• To investigate the role of electron-phonon coupling (EPC) Berry curvature in strain-induced effects.
• To develop a general theory for strain-controlled ferroelectric phase transitions.

Main Methods:

• Density-functional perturbation theory (DFPT) calculations.
• Analysis of electron-phonon coupling (EPC) Berry curvature.
• Model analysis of strain effects on interatomic force matrices.
• Ab initio calculations on benchmark materials like BiOCl monolayer.

Main Results:

• Berry curvature of EPC is pivotal in the interatomic force matrix.
• External strain reverses EPC Berry curvature polarity via band inversion in degenerate electronic systems.
• This reversal directly leads to phonon softening, inducing ferroelectricity.
• The developed theory accurately describes BiOCl monolayer and generalizes to other materials.

Conclusions:

• Strain-induced ferroelectricity is governed by the quantum geometry of EPC Berry curvature.
• This mechanism provides a microscopic understanding of lattice dynamics and FE phase transitions.
• The findings offer a new perspective on designing and controlling ferroelectric materials.