Observation of non-Hermitian boundary induced hybrid skin-topological effect excited by synthetic complex frequencies

TL;DR

This paper experimentally observes the hybrid skin-topological effect (HSTE) in a transmission line network using synthetic complex frequencies, revealing asymmetric transmission and boundary effects in non-Hermitian topological systems.

Contribution

It provides the first experimental demonstration of HSTE with synthetic complex frequency excitations, clarifying boundary effects and the role of non-Hermitian boundary conditions.

Findings

HSTE induces asymmetric transmission within the topological band gap

Corner states can originate from non-chiral edge states due to boundary energy shifts

HSTE states can be manipulated by boundary non-Hermitian distribution

Abstract

The hybrid skin-topological effect (HSTE) has recently been proposed as a mechanism where topological edge states collapse into corner states under the influence of the non-Hermitian skin effect (NHSE). However, directly observing this effect is challenging due to the complex frequencies of eigenmodes. In this study, we experimentally observe HSTE corner states using synthetic complex frequency excitations in a transmission line network. We demonstrate that HSTE induces asymmetric transmission along a specific direction within the topological band gap. Besides HSTE, we identify corner states originating from non-chiral edge states, which are caused by the unbalanced effective onsite energy shifts at the boundaries of the network. Furthermore, our results suggest that whether the bulk interior is Hermitian or non-Hermitian is not a key factor for HSTE. Instead, the HSTE states can be realized and relocated simply by adjusting the non-Hermitian distribution at the boundaries. Our research has deepened the understanding of a range of issues regarding HSTE, paving the way for advancements in the design of non-Hermitian topological devices.