Higher-order non-Hermitian skin effect

A unique feature of non-Hermitian systems is the skin effect, for which an extensive number of boundary modes appear in the presence of boundaries. Here, the authors discover higher-order counterparts of the non-Hermitian skin effect that exhibit new boundary physics. As a prime example, the second-order skin effect in two dimensions hosts corner skin modes induced by spatial symmetry protected non-Hermitian topology, which contrasts with both the conventional skin effect and Hermitian higher-order topological phases.