Magnetic topological insulators: from magnetically doped to intrinsic

A topological insulator (TI) is a nonmagnetic insulator carrying metallic surface electronic states topologically protected by the time-reversal symmetry (TRS). Many exotic quantum effects predicted for TIs, however, need the TRS to be broken by acquired magnetic order. A remarkable example is the quantum anomalous Hall (QAH) effect—a quantum Hall effect induced by spontaneous magnetization instead of an external magnetic field. Magnetically doped TIs are notorious “dirty” materials. An ideal magnetic TI is an intrinsic one, namely a stoichiometric compound with orderly arranged and exchange-coupled magnetic atoms which features a magnetically ordered ground state, but becomes a TI when the TRS recovers above the magnetic ordering temperature. In this talk, I will introduce our past works on the QAH effect in magnetically doped TIs and our recent progress on searching for an intrinsic magnetic topological insulator. I will also discuss how to achieve the QAH effect at higher temperature and how to construct other topological states of matter by engineering magnetic TIs.