Novel defect control and chemical doping strategies are discovered to suppress the detrimental bulk conduction in the antiferromagnetic topological insulators MnBi2Te4 and MnBi4Te7. The results of this work will aid the observation of exotic topological quantum states, which have potential applications in future electronic devices.
MnBi2Te4 is the first topological insulator discovered with an intrinsic magnetic ordering. A topological insulator should have an insulating bulk and a conductive surface. A high defect density is a major obstacle in observing topological quantum phenomena because the defects give rise to bulk metallic conductivity, which prevents the measurement of quantum transport through the topological surface states. Density functional theory calculations of defect and dopant properties in MnBi2Te4 and MnBi4Te7 combined with carrier statistics calculations provide understanding of the main defect formation mechanism, which is intimately related to the internal strain in these layered materials. This novel understanding enables design strategies for tuning bulk conductivity by precisely controlling defects and dopants. The defect management approach is further validated by experimental synthesis and transport measurements. A new acceptor dopant, sodium, and specific growth conditions are proposed to minimize bulk conductivity for the measurement of quantum transport through topological surface states.
