  We demonstrate the creation of robust localized zero-energy states that are
induced into topologically trivial systems by insertion of a PT-symmetric
defect with local gain and loss. A pair of robust localized states induced by
the defect turns into zero-energy modes when the gain-loss contrast exceeds a
threshold, at which the defect states encounter an exceptional point. Our
approach can be used to obtain robust lasing or perfectly absorbing modes in
any part of the system.

Optics;Other Condensed Matter