124th CEMS Colloquium

Title

Quantum transport in heterostructure of magnetic topological insulator

Abstract

A topological insulator is a material whose interior is an insulator while its surface is a gapless metal. The gapless surface state is ensured by the non-trivial topology of the band structure and time-reversal symmetry. The quantum anomalous Hall effect (QAHE) is one of the hallmark phenomena arising from the non-trivial topology of magnetic topological insulators with broken time-reversal symmetry. The Hall resistance quantizes to the quantum resistance h/e² and the longitudinal resistance vanishes even at the zero magnetic field.

We have developed heterostructure thin films of magnetic topological insulators where the magnetic element Cr was doped only near the topological surface states and observed QAHE successfully. The heterostructure allowed us to measure the Hall resistance quantization with an accuracy of ten parts per billion [2]. The high accuracy nearly satisfies the requirements for the practical resistance calibration service, demonstrating a zero-field operable quantum resistance standard.

Furthermore, the heterostructure allowed us to observe the Laughlin charge pump, an adiabatic charge pump associated with the increment in the magnetic flux. We observed that the charge pump occurs between the inner and outer electrodes of a Corbino disk sample in response to alternating magnetic fields. The amount of the pumped charge is accounted for by the quantized surface Hall conductivity.

[1] M. Mogi et al., Appl. Phys. Lett. 107, 182401 (2015).
[2] Y. Okazaki et al., Nat. Phys. 18, 25 (2022).
[3] M. Kawamura et al., Nat. Phys. 19, 333 (2023).