  Hermitian topological materials are characterized by the nontrivial relation
between topological numbers and edge modes, i.e. the bulk-boundary
correspondence. In non-Hermitian systems, the conventional correspondence
breaks down. Instead, in the non-Hermitian Su-Schrieffer-Heeger model, the
non-Bloch bulk-boundary correspondence, which is the relation between the
non-Bloch winding number and the non-Hermitian skin effect, is proposed by S.
Yao and Z. Wang. We introduce the non-Bloch polarization as a topological
quantity to detect the non-Hermitian skin effect. Moreover, we also discuss the
non-Bloch bulk-boundary correspondence in two-dimensional systems using the
non-Bloch polarization with spiral boundary conditions.
