Experimental observation of interconversion of non-Hermitian skin effect and Anderson localization in a nonreciprocal topological circuit based on Aubry-André model

The non-Hermitian skin effect (NHSE) is a phenomenon that emerges in non-Hermitian systems. Non-Hermitian systems can be flexibly realized by introducing non-Hermitian terms in circuits. In topolectrical circuits, nonreciprocal hopping is realized by scaling linear elements, which introduces non-Hermitian terms. In this work, we report the experimental realization of the NHSE in such nonreciprocal circuits. By introducing a quasiperiodic potential, the experimental realization of the interconversion between the NHSE and Anderson localization (AL) is observed in a nonreciprocal quasiperiodic circuit based on the nonreciprocal Aubry-Andr\'e (AA) model, which undergoes a skin-effect--localization phase transition depending on the strength of the quasiperiodic potential. In addition, we design and fabricate a dedicated circuit board with preset component slots, enabling continuous tuning of circuit parameters without the need for multiple circuit boards. This flexible platform allows us to experimentally identify the phase-transition point between the NHSE and AL. Our results fill an important gap in previous studies, where this transition point had not been precisely characterized. Our circuit system also provides a simpler platform to explore localization phenomena in nonreciprocal systems.