Topological magnetoelectric response in ferromagnetic axion insulators

Area of Science:

• Condensed Matter Physics
• Materials Science
• Topological Quantum Phenomena

Background:

• The topological magnetoelectric effect (TME) is a key prediction of topological field theory for emergent topological phenomena.
• Direct experimental observation of TME has been hindered by the complex magnetic configurations needed to gap surface states.

Purpose of the Study:

• To theoretically propose a realistic material system and geometry for realizing the topological magnetoelectric effect.
• To identify a viable pathway for the direct experimental observation of TME.

Main Methods:

• Theoretical modeling of axion insulators in a ferromagnetic configuration, specifically the MnBi2Te4/(Bi2Te3)n family.
• Design of a triangular prism geometry to magnetically gap all surface states.
• Analysis of surface Hall currents and orbital moments under an applied electric field.

Main Results:

• Demonstrated that axion insulators with simple ferromagnetic order can host TME.
• Proposed a triangular prism geometry where all surface states are magnetically gapped.
• Predicted a nearly half-quantized orbital moment and a gapless chiral hinge mode under an electric field, distinguishable by field reversal.

Conclusions:

• The MnBi2Te4/(Bi2Te3)n material family offers a promising platform for observing TME.
• The proposed geometry and predicted signatures facilitate the distinction of orbital magnetization from different topological origins.
• This theoretical work provides a direct route towards the experimental realization of the topological magnetoelectric effect.