Transport measurement of ferromagnetic insulator/topological insulator van der Waals heterostructures

Abstract

Quantum anomalous Hall effect can be realized in topological insulators with breaking time-reversal symmetry by introducing magnetism, which can be achieved by proximity effect between ferromagnetic insulator/topological insulator (FMI/TI) heterostructures. Compared with synthetic FMI/TI heterostructures, the system fabricated by layers stacked owns better quality for the absence of chemical diffusion and lattice matching. In this thesis, two different FMI/TI heterostructures CrBr₃/Bi₂Se₃ and CrGeTe₃/BiSbTeSe₂ are fabricated by dry transfer method, and the transport properties of these systems are investigated. Both anomalous Hall effect (AHE) and topological Hall effect (THE) are observed in these two systems. Compared with the curie temperature and the coercive field of the bare FMI (CrBr₃ or CrGeTe₃), the two critical values show an enhancement in the two FMI/TI heterostructures, which is viewed as a proof of magnetic proximity effect induced magnetism. Moreover, the negative magnetoresistance is observed in some CrBr₃/Bi₂Se₃ heterostructures but not observed in CrGeTe₃/BiSbTeSe₂ heterostructures. In addition, the sign change of AHE is observed with changing temperature in both systems or applied gate voltage in CrGeTe₃/BiSbTeSe₂ systems, but the mechanism is unclear and needs further study.

Date of Award	2024
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Jiannong WANG (Supervisor)