Condense Matter Physics Seminar: MnBi2Te4.nBi2Te3: a happy marriage of magnetism and topology, by Dr. Ni Ni of UCLA

April 5, 2021 @ 3:00 pm – 4:00 pm America/New York Timezone

Title: MnBi2Te4.nBi2Te3: a happy marriage of magnetism and topology

Speaker: Dr. Ni Ni, UCLA

Time: April 5, 2021 03:00 PM Eastern Time (US and Canada)

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Abstract: Magnetic topological material provides a great platform for discovering new topological states, such as the axion insulators, the Chern insulators, and the 3D quantum anomalous Hall (QAH) insulators. Recently, MnBi2Te4 was discovered to be the first material realization of an intrinsic antiferromagnetic topological insulator (TI) where the QAH effect was observed at a record high temperature in its two-dimensional limit. Since the interplay of the magnetism and band topology determines their topological natures, understanding and manipulating the magnetism inside magnetic TIs will be crucial. In this talk, I will present our discovery of two new magnetic topological materials MnBi2Te4.nBi2Te3 (n=1 and 3) which consist of alternating [MnBi2Te4] and n[Bi2Te3] layers [1, 2]. I will show that by reducing the interlayer magnetic coupling with the increasing number of spacer [Bi2Te3] layers, MnBi2Te4.nBi2Te3 can be tuned from Z2 antiferromagnetic TIs (n=0,1,2) to ferromagnetic axion insulators. Furthermore, I will show that a continuous fine control of the magnetism in MnBi4Te7 can be made by Sb doping where an AFM to FM switching emerges due to the formation of the Mn/Sb antisite disorders [3]. Our study provides a rare tunable material platform to investigate various emergent phenomena arising from the interplay of magnetism and band topology.


My research focuses on the characterization of physical properties and structures of materials through thermodynamic, transport, X-ray and neutron measurements, with an emphasis on the design, synthesis and crystal growth of new materials. Our interests span a wide spectrum of materials, from intermetallics to oxides, especially superconductors and strongly correlated electron systems showing unusual electronic and magnetic ground states that can be perturbed by chemical doping, applied pressure or magnetic field. We aim at synthesizing new materials with nontrivial properties, characterizing quantum phases, and examining the different energy scales in solids. The interplay of magnetism, superconductivity and structure will be of particular interest.