Exchange-bias-driven and Interaction-driven Quantum Anomalous Hall Effect in Topological Insulator Heterostructures

Quantum anomalous Hall (QAH) state is a magnetic topological state with zero longitudinal resistance and quantized Hall resistance, occurring in the absence of external magnetic fields due to spontaneously broken time-reversal symmetry. The QAH effect has now been realized in several different classes of two-dimensional materials, including magnetically (Cr or V) doped (Bi,Sb)₂Te₃, MnBi₂Te₄, and Moire materials of graphene and transition metal dichalcogenides. Despite of these impressive progress, the temperature at which the QAH effect is observed is still limited to a few Kelvins. Two general approaches are expected to enhance this critical temperature [1]: (1) high-quality heterostructures between topological insulators and high Curie temperature ferromagnetic insulator; and (2) new Moire systems. In this talk, I will describe our theoretical efforts along these directions. (1) The strong exchange bias between MnBi2Te4 and CrI3 can give rise to the electrically tunable QAH effect in MnBi2Te4/CrI3 heterostructure [2]. (2) Isolated topologically non-trivial Moire mini-bands can be formed for a topological insulator film under a Moire superlattice and Coulomb interaction can drive this system into the QAH state when the non-trivial Moire mini-band is half filled [3].