Zero-field edge plasmons in a magnetic topological insulator

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• The quantum anomalous Hall effect (QAHE) in ferromagnetic topological insulators enables dissipationless currents at zero magnetic field.
• Previous studies relied on low-frequency transport measurements, which can be complicated by parallel conduction and unintended edge channels.
• Robust chiral edge channels are crucial for realizing practical applications of QAHE materials.

Purpose of the Study:

• To move beyond transport measurements for investigating QAHE materials.
• To probe the microwave response of magnetic topological insulator thin films.
• To identify signatures of intrinsic chiral edge channels and measure their properties.

Main Methods:

• Fabrication of magnetised Cr-(Bi,Sb)₂Te₃ thin film disks.
• Non-contact microwave response measurements.
• Analysis of spectral features associated with chiral edge plasmons.

Main Results:

• Identification of distinct spectral features linked to chiral edge plasmons in the microwave response.
• Confirmation that robust edge channels are intrinsic to the Cr-(Bi,Sb)₂Te₃ material system.
• Determination of the velocity of edge excitations without direct electrical contact.

Conclusions:

• Microwave spectroscopy provides a powerful, contact-free method for characterizing chiral edge states in magnetic topological insulators.
• The observed chiral edge plasmons confirm the presence of robust, intrinsic edge channels.
• These findings pave the way for developing novel on-chip electronic components, such as zero-field microwave circulators.