A van der Waals antiferromagnetic topological insulator with weak interlayer magnetic coupling

Magnetic topological insulators (TI) provide an important material platform to explore quantum phenomena such as quantized anomalous Hall effect and Majorana modes, etc. Their successful material realization is thus essential for our fundamental understanding and potential technical revolutions. By realizing a bulk van der Waals material MnBi₄Te₇ with alternating septuple [MnBi₂Te₄] and quintuple [Bi₂Te₃] layers, we show that it is ferromagnetic in plane but antiferromagnetic along the c axis with an out-of-plane saturation field of ~0.22 T at 2 K. Our angle-resolved photoemission spectroscopy measurements and first-principles calculations further demonstrate that MnBi₄Te₇ is a Z₂ antiferromagnetic TI with two types of surface states associated with the [MnBi₂Te₄] or [Bi₂Te₃] termination, respectively. Additionally, its superlattice nature may make various heterostructures of [MnBi₂Te₄] and [Bi₂Te₃] layers possible by exfoliation. Therefore, the low saturation field and the superlattice nature of MnBi₄Te₇ make it an ideal system to investigate rich emergent phenomena.