Bulk-boundary correspondence in non-Hermitian Hopf-link exceptional line semimetals
Zhicheng Zhang, Zhesen Yang, Jiangping Hu
Abstract
We consider a three-dimensional non-Hermitian exceptional line semimetal model and take open boundary conditions in the $x$, $y$, and $z$ directions separately. In each case, we calculate the parameter regions where the bulk-boundary correspondence is broken. The breakdown of the bulk-boundary correspondence is manifested by the deviation from unit circles of generalized Brillouin zones (GBZs) and the discrepancy between spectra calculated with open boundary conditions (OBCs) and periodic boundary conditions (PBCs). The consistency between OBC and PBC spectra can be recovered if the PBC spectra are calculated with GBZs. We use both unit-circle Brillouin zones (BZs) and GBZs to plot the topological phase diagrams. The systematic analysis about the differences between the two phase diagrams suggests that it is necessary to use GBZs to characterize the bulk-boundary correspondence of non-Hermitian models.