Bulk-entanglement spectrum correspondence in $PT$- and $PC$-symmetric topological insulators and superconductors

In this study, we discuss a new type of bulk-boundary correspondence which holds for topological insulators and superconductors when the parity-time ($PT$) and/or parity-particle-hole ($PC$) symmetry are present. In these systems, even when the bulk topology is nontrivial, the edge spectrum is generally gapped, and thus the conventional bulk-boundary correspondence does not hold. We find that, instead of the edge spectrum, the single-particle entanglement spectrum becomes gapless when the bulk topology is nontrivial: i.e., the bulk-entanglement spectrum correspondence holds in $PT$- and/or $PC$-symmetric topological insulators and superconductors. After showing the correspondence using K-theoretic approach, we provide concrete models for each symmetry class up to three dimensions where nontrivial topology due to $PT$ and/or $PC$ is expected. An implication of our results is that, when the bulk topology under $PT$ and/or $PC$ symmetry is nontrivial, the non-interacting many-body entanglement spectrum is multiply degenerate in one dimension and is gapless in two or higher dimensions.