Observation of anomalous non-Hermitian skin effect in electric circuits

Non-Hermitian skin effect allows the bulk states to collapse toward the boundaries, which originates from the nontrivial energy spectral topology described by nonzero spectral windings. Recent theoretical studies have revealed that the spectral windings do not accurately predict the skin effect in some cases, which has not yet been confirmed in the experiment. Here, we find that this abnormal phenomenon can also exist in a bilayer Hatono-Nelson chain, which is caused by the unidirectional coupling between two chains, where the energies are decoupled, but the wave functions are not. We implement this theoretical model in electric circuits and observe anomalous skin effects by measuring the localized voltage distributions. Our findings deepen the understanding of the skin effect in multichain systems and may inspire a more complete non-Hermitian theory.