Orbital longitudinal magnetoelectric coupling in rhombohedral multilayer graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Magnetoelectric coupling allows control of magnetic properties with electric fields.
• Typically observed in heavy elements due to strong spin-orbit coupling.
• Recent experiments show longitudinal magnetoelectric coupling (LMC) in rhombohedral-stacked pentalayer graphene without spin-orbit coupling.

Purpose of the Study:

• Develop a microscopic theory for LMC in layered quantum materials.
• Identify the role of quantum geometry in controlling LMC.
• Investigate magnetoelectric properties in rhombohedral multilayer graphene.

Main Methods:

• Microscopic theoretical framework development.
• Analysis of quantum geometry effects in layered materials.
• Focus on rhombohedral multilayer graphene systems.

Main Results:

• Identified 'layer-space' quantum geometry as a key control for LMC.
• Demonstrated interplay between LMC and valley-polarized order.
• Observed butterfly-shaped magnetic hysteresis controlled by electric fields, indicating multiferroic valley order.
• Discovered nonlinear LMC and second-order nonlinear electric dipole generation.

Conclusions:

• The theoretical framework quantitatively explains LMC in rhombohedral multilayer graphene.
• Emergent magnetoelectric properties arise from the interplay of LMC and valley order.
• Rhombohedral multilayer graphene exhibits unique multiferroic behavior controllable by external fields.