# Zero-field Edge Magnetoplasmons in a Magnetic Topological Insulator

## TL;DR

This paper demonstrates the detection of chiral edge magnetoplasmons in a magnetized topological insulator, providing a contactless method to study edge states relevant for quantum anomalous Hall effect applications.

## Contribution

It introduces microwave response measurements to identify edge magnetoplasmons in a magnetic topological insulator, advancing beyond traditional transport techniques.

## Key findings

- Identification of edge magnetoplasmons in a magnetized TI disk.
- Measurement of edge excitation velocities without contacting the sample.
- Potential development of on-chip microwave circulators based on TIs.

## Abstract

Incorporating ferromagnetic dopants, such as chromium or vanadium, into thin films of the three-dimensional (3D) topological insulator (TI) (Bi,Sb)2Te3 has recently led to the realisation of the quantum anomalous Hall effect (QAHE), a unique phase of quantum matter. These materials are of great interest, since they may support electrical currents that flow without resistance via edge channels, even at zero magnetic field. To date, the QAHE has been investigated using low-frequency transport measurements. However, transport requires contacting the sample and results can be difficult to interpret due to the presence of parallel conductive paths, via either the bulk or surface, or because additional non-chiral edge channels may exist. Here, we move beyond transport measurements by probing the microwave response of a magnetised disk of Cr-(Bi,Sb)2Te3. We identify features associated with chiral edge magnetoplasmons (EMPs), a signature that robust edge-channels are indeed intrinsic to this material system. Our results provide a measure of the velocity of edge excitations without contacting the sample, and pave the way for a new, on-chip circuit element of practical importance: the TI, zero-field microwave circulator.