Topolectrical circuit realization of topological corner modes

TL;DR

This paper demonstrates the experimental realization of topological corner modes in a topolectrical circuit, providing a classical platform to study quantum topological states protected by symmetries.

Contribution

The authors design and measure a topolectrical circuit that exhibits topological corner modes, bridging quantum topological insulators and classical electrical systems.

Findings

Corner modes appear as boundary resonances in impedance profiles.

The circuit design confirms the symmetry-protected nature of the modes.

The work links quantum topological concepts with classical circuit realizations.

Abstract

Quantized electric quadrupole insulators have recently been proposed as novel quantum states of matter in two spatial dimensions. Gapped otherwise, they can feature zero-dimensional topological corner mid-gap states protected by the bulk spectral gap, reflection symmetries and a spectral symmetry. Here we introduce a topolectrical circuit design for realizing such corner modes experimentally and report measurements in which the modes appear as topological boundary resonances in the corner impedance profile of the circuit. Whereas the quantized bulk quadrupole moment of an electronic crystal does not have a direct analogue in the classical topolectrical-circuit framework, the corner modes inherit the identical form from the quantum case. Due to the flexibility and tunability of electrical circuits, they are an ideal platform for studying the reflection symmetry-protected character of corner modes in detail. Our work therefore establishes an instance where topolectrical circuitry is employed to bridge the gap between quantum theoretical modelling and the experimental realization of topological band structures.