Phonon Magnetic Moment from Electronic Topological Magnetization

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Mechanics

Background:

• Traditional theories describe chiral phonon magnetic moments via circular motion of Born effective charge.
• These theories typically predict small, fractional magnetic moment values relative to the nuclear magneton.

Purpose of the Study:

• To investigate the adiabatic evolution of electronic states induced by chiral phonons.
• To derive a more accurate model for electronic orbital magnetization originating from lattice vibrations.
• To identify new contributions to magnetic moments in chiral phonon systems.

Main Methods:

• Analyzing the adiabatic evolution of electronic states under chiral phonon vibrations.
• Deriving electronic orbital magnetization using topological concepts (second Chern form).
• Investigating the role of k-resolved Born effective charge and phonon-modified electronic energy.

Main Results:

• Electronic orbital magnetization is described by a topological second Chern form.
• The traditional theory requires refinement with k-resolved Born effective charge.
• A new contribution arises from phonon-modified electronic energy and momentum-space Berry curvature.
• The second Chern form can diverge near Yang's monopoles, exemplified in gapped graphene.
• Large magnetic moments are found for optical phonons in topological materials, with significant nontopological contributions.

Conclusions:

• The study provides a refined theoretical framework for magnetic moments in chiral phonons.
• The findings highlight the topological nature of electronic orbital magnetization induced by lattice vibrations.
• The results offer insights into experimental observations in topological materials and gapped graphene systems.