Topolectrical-circuit octupole insulator with topologically protected corner states

TL;DR

This paper reports the first experimental realization of a three-dimensional octupole topological insulator using classical electric circuits, demonstrating topologically protected corner states and robustness against disorder.

Contribution

It introduces a novel experimental setup for realizing and observing octupole topological phases in 3D electric circuits, extending higher-order topological insulators research.

Findings

Observation of octupole topological states localized at corners

Demonstration of robustness of these states against disorder

Construction of 3D topolectrical circuits for topological phase realization

Abstract

Recent theoretical studies have extended the Berry phase framework to account for higher electric multipole moments, quadrupole and octupole topological phases have been proposed. Although the two-dimensional quantized quadrupole insulators have been demonstrated experimentally, octupole topological phases have not previously been observed experimentally. Here we report on the experimental realization of classical analog of octupole topological insulator in the electric circuit system. Three-dimensional topolectrical circuits for realizing such topological phases are constructed experimentally. We observe octupole topological states protected by the topology of the bulk, which are localized at the corners. Our results provide conclusive evidence of a form of robustness against disorder and deformation, which is characteristic of octupole topological insulators. Our study opens a new route toward higher-order topological phenomena in three-dimensions and paves the way for employing topolectrical circuitry to study complex topological phenomena.