Observation of monopole topological mode.

Area of Science:

• Condensed Matter Physics
• Topological Materials
• Acoustic Metamaterials

Background:

• The theoretical existence of magnetic monopoles has long been predicted, with potential implications for fundamental physics.
• Topological zero modes, such as kinks and vortices, have been observed, but magnetic monopoles have remained elusive.
• Dirac equations describe fundamental particle behavior, and their topological properties are key to understanding exotic states.

Purpose of the Study:

• To experimentally realize and characterize magnetic monopole solutions within a synthetic material.
• To investigate the construction of monopole and multi-monopole states using band theory.
• To explore the relationship between bulk topology and defect properties in higher dimensions.

Main Methods:

• Constructing monopole and multi-monopole solutions by gapping three-dimensional Dirac points in hedgehog mass configurations within band theory.
• Designing and fabricating an optimized Dirac acoustic crystal with structural modulation in all solid angles.
• Experimentally demonstrating the monopole bound state within the acoustic crystal.

Main Results:

• Successful experimental demonstration of a magnetic monopole bound state in a synthetic acoustic crystal.
• The observed monopole mode exhibits optimal scaling behavior, with modal spacing inversely proportional to the cubic root of the modal volume.
• This work establishes a connection between bulk topological properties and defect characteristics.

Conclusions:

• The experimental realization of the magnetic monopole bound state completes the trilogy of kink, vortex, and monopole zero modes.
• This research provides a platform for studying topological phenomena in engineered systems.
• The findings open new avenues for exploring higher-dimensional bulk-topological-defect correspondence.