Axion Electrodynamics — 3D Topological Insulator
Topological Magnetoelectric Effect · θ = π · Quantized Hall Response
Parameters
Surface gap Δ (meV):
30
Magnetic coating M (Tesla):
0.5
θ / π:
1.00
Chemical potential μ (meV):
0
L = L
Maxwell
+ (θe²/2πh) E·B
σ
xy
= (n + θ/2π) · e²/h
At θ=π: σ
xy
= (n + ½) e²/h
The axion angle θ=π is topologically protected by T-symmetry. Magnetic coating breaks T, gaps the surface, and induces a half-quantized Hall conductance.
Top surface
Bottom surface
Bulk gap