Observation of non-Hermitian topological disclination states and charge fractionalization

TL;DR

This paper reports the first experimental observation of non-Hermitian topological disclination states in electric circuits, revealing fractional charges and zero-energy states induced by gain and loss, advancing active topological photonics.

Contribution

It provides the first experimental evidence of non-Hermitian topological disclination states and fractional charges in electric circuits, expanding the understanding of non-Hermitian topological phenomena.

Findings

Observation of topological disclination states induced by gain and loss

Visualization of mode profiles and localization effects

Identification of zero-energy disclination states without fractional charge

Abstract

There has been significant interest in exploring topological disclination states, which effectively probe the band topology of the host material beyond the conventional bulk-edge correspondence. While most studies in this area have primarily focused on Hermitian systems, recent theoretical work predicts that non-Hermiticity can drive topological phase transitions and host topological disclination states associated with fractional charge. However, no experimental observations have been reported to date. Here, we report the first experimental observation of topological disclination states in electric circuits, induced solely by gain and loss. Through admittance matrix measurements and eigenstate analysis, we confirm their emergence and compute the corresponding fractional charge. Moreover, the disclination mode profile and localization effect can be directly visualized via monochromatic field excitation. Additionally, we demonstrate the emergence of degenerate zero-energy topological disclination states, devoid of fractional charge, in distinct non-Hermitian geometries. Our findings open the possibility of non-Hermiticity-induced fractional charges in two-dimensional non-Hermitian lattices, which may pave the way for advancements in active topological photonic devices.