Extended states isolated in the band gap in non-Hermitian electrical circuits

Extended states are usually in the continuum spectrum. Recent studies revealed that the extended states can be isolated in the band gap, which has not yet been confirmed in electric circuits. In this work, based on the non-Hermitian Su-Schrieffer-Heeger electric circuits, we realize the extended states that are isolated in the band gap, which can be attributed to the non-Hermitian skin effect. In particular, these extended states are topological with the quantized topological invariants. The non-Hermitian skin effect and topological extended states are confirmed directly by the measured voltage responses. We further show the extended states are robust against weak disorders. Our system provides a tunable platform to explore alternative phenomena arising from the isolated topological extended states.