Large dynamical axion field in topological antiferromagnetic insulator Mn$_2$Bi$_2$Te$_5$

Understand

The dynamical axion field is a new state of quantum matter where the magnetoelectric response couples strongly to its low-energy magnetic fluctuations.

• It is fundamentally different from an axion insulator with a static quantized magnetoelectric response.
• The dynamical axion field exhibits many exotic phenomena such as axionic polariton and axion instability.
• However, these effects have not been experimentally confirmed due to the lack of proper topological magnetic materials.