Two-Dimensional Density-Matrix Topological Fermionic Phases: Topological Uhlmann Numbers
Two-Dimensional Density-Matrix Topological Fermionic Phases: Topological Uhlmann Numbers
We construct a topological invariant that classifies density matrices of symmetry-protected topological orders in two-dimensional fermionic systems. As it is constructed out of the previously introduced Uhlmann phase, we refer to it as the topological Uhlmann number n_{U}. With it, we study thermal topological phases in several two-dimensional models of …