Tunable non-Hermitian skin effect via gain and loss

We theoretically investigate a tunable non-Hermitian skin effect in systems with gain and loss and find that the bipolar (quadripolar) non-Hermitian skin effect is characterized by topological invariants in one (two)- dimensional systems. We also find the partial non-Hermitian skin effect with the coexistence of localized states and extended states. Both types of the non-Hermitian skin effect have not yet been predicted together in a single system. In addition, we propose a feasible experimental scheme for our model that is realizable in electric circuits. Our investigation unveils another type of non-Hermitian skin effect and enhances the tunability of the non-Hermitian systems by gain and loss other than the conventional nonreciprocal hopping.