Precise Quantization of the Anomalous Hall Effect near Zero Magnetic Field

Area of Science:

• Condensed matter physics
• Materials science
• Quantum phenomena

Background:

• The quantum anomalous Hall effect (QAHE) is a quantum phenomenon observed in magnetic topological insulators.
• Achieving precise QAHE with minimal external magnetic fields is crucial for spintronic applications.

Purpose of the Study:

• To investigate the QAHE in ferromagnetic topological insulator thin films.
• To characterize the transport properties and identify factors causing deviations from ideal QAHE.
• To explore potential applications of observed phenomena, such as cooling.

Main Methods:

• Fabrication of a three-dimensional topological insulator thin film with ferromagnetic doping.
• Measurement of Hall resistance and longitudinal resistivity near zero magnetic field.
• Utilizing nonlocal measurements to confirm chiral edge transport.
• Analyzing temperature dependence of resistivity to identify carrier types.
• Employing deviations as a thermometer to demonstrate magnetocaloric effect.

Main Results:

• Observation of a nearly ideal QAHE with exact Hall resistance quantization to 1 part in 10,000.
• Longitudinal resistivity consistently below 1 Ω/sq.
• Explicit confirmation of chiral edge transport via nonlocal measurements.
• Identification of thermally activated carriers as the cause of deviations, following an Arrhenius law.
• Demonstration of an unexpected magnetocaloric effect.

Conclusions:

• Ferromagnetic doping in topological insulator thin films enables near-ideal QAHE.
• Chiral edge states are robust and can be confirmed through nonlocal transport measurements.
• The magnetocaloric effect observed can be utilized for cooling, potentially reaching near-perfect quantization.