Topological Matters

A topological insulator is a material that behaves as an insulator in the bulk but shows exotic conducting states on its surface which are protected by the time-reversal symmetry. The interplay of magnetism and topology is a key research subject in condensed matter physics, which offers great opportunities to explore emerging new physics, such as the quantum anomalous Hall effect, axion electrodynamics, and Majorana fermions. As a new extension of the current study of topological insulators, antiferromagnetic topological insulators (AFMTI), in which the antiferromagnetic long-range order in a topological insulator spontaneously breaks time-reversal symmetry. Proposed by most cutting-edge research, MnBi2Te4, GdBiPt are two promising examples of this topological class. The as-grown MnBi2Te4 single crystal exhibits a van der Waals layered structure, which is composed of septuple Te-Bi-Te-Mn-Te-Bi-Te sequences. However, this compound is not ideal from the perspective of inorganic chemistry, since cation intermixing is ubiquitous in such structure type, and thus non-stoichiometry has been noticed in several spectroscopy experiments. Forthcoming endeavors in our group can be focused on optimizing this material by atomic substitution with rare-earth elements, which migh be able to solve the intermixing problem and meanwhile exhibt a gapped Dirac-cone-like dispersion, suggested by first-principles calculations.