Entanglement spectrum of gapless topological phases: A case study with topological superconductors

Using bulk gapless topological superconductors in both 1D and 2D as free fermion model examples, we demonstrate the power of subsystem correlation spectrum (the spectrum of correlation matrix), or equivalently the entanglement spectrum for the case of free fermions, in characterizing the topology of the nontrivial ground state. For the systems considered, we show that signatures of the low-energy spectrum, including both the edge modes and the bulk modes, appear in the correlation spectrum, albeit with different behaviors. This work generalizes the 2D Li-Haldane entanglement spectrum characterization of topological edge states to 2D topological systems with gapless bulk.