Effects of interactions on the topological classification of free fermion systems
Effects of interactions on the topological classification of free fermion systems
We describe in detail a counterexample to the topological classification of free fermion systems. We deal with a one-dimensional chain of Majorana fermions with an unusual $T$ symmetry. The topological invariant for the free fermion classification lies in $\mathbb{Z}$, but with the introduction of interactions the $\mathbb{Z}$ is broken to …