Figure 1: SPT phase in 2D with Z2 and time-reversal symmetry (
).
).From: Symmetry-protected topological phases from decorated domain walls
A snapshot of the ground state wave function: blue and grey are oppositely directed domains of the Z2 symmetry. The ground state preserves the Z2 symmetry since it is a superposition of domain configurations. The domain walls themselves (black lines) are in a d=1 SPT phase (the Haldane/AKLT phase) protected by time reversal symmetry. When they end at the edge of the system they create Kramers doublets, leading to a gapless edge state.
