Combining magnetism and topology: from magnetic doping and proximity effect to novel interfaces and intrinsic materials

Speaker

Dr. Mikhail M. Otrokov

Instituto de Nanociencia y Materiales de Aragón (INMA), 

CSIC-Universidad de Zaragoza, Spain

Time

10：00am, September 26, 2025

Place

Conference room on 3F, Material Science and Research Building

Mikhail Otrokov (born in 1984) obtained his PhD in Condensed Matter Physics in 2011 at Tomsk State University (Russia). Soon after that he moved to San Sebastian (Spain) as a post-doctoral researcher, first at the Donostia International Physics Center and then at the Materials Physics Center. In 2018, he got an independent Research Fellow position in Ikerbasque - Basque Foundation for Science in San Sebastian (Spain). Since 2023, he is a research scientist in the Institute of Nanoscience and Materials of Aragon in Zaragoza (Spain). His expertise is the computational materials science using the density functional theory, with the current research activity mainly focused on magnetic topological insulators, although he is also interested in the electronic structure and magnetism of 2D materials, metal-organic systems, rare-earth intermetallics, and others. His paper on the discovery of the first intrinsic magnetic topological insulator was distinguished by the “Frontiers of Science Award” in 2023.

Abstract

In this talk, I will overview the developments in the field of magnetic topological insulators (MTIs) that led to the discovery of the intrinsic MTIs of the MnBi₂Te₄ family that attracts a great deal of attention nowadays. First, to describe the context in which materials such as MnBi₂Te₄ appeared in the research arena, I will discuss the magnetic doping and magnetic proximity effect approaches of introducing magnetism into a TI. Then, the two types of novel interfaces involving MnBi₂Te(Se)₄ compounds will be discussed, as they are expected to show certain advantages over the latter two approaches.

Next, the discovery of intrinsic MTIs of the MnBi₂Te family will be overviewed in great detail [1-4]. The appearance of these materials opens a new field that focuses on intrinsically magnetic stoichiometric compounds: several MnBi₂Te₄-derived MTIs were synthesized right away [5], such as (MnBi₂Te₄)·n(Bi₂Te₃), MnBi_2−xSb_xTe₄, (MnSb₂Te₄)·n(Sb₂Te₃), Mn₂(Bi,Sb)₂Te₅, and MnBi₂Se₄. As a result, MnBi₂Te₄ and related compounds have been predicted to be a platform for realizing high-order topological insulator and superconductor states, Weyl semimetal phase, skyrmions, quantized magnetoeletric coupling, and Majorana fermions. Moreover, MnBi₂Te₄-based systems are predicted and/or observed to show 12 different types of Hall effect [6,7], some of them are fundamentally new, such as the layer Hall effect [7]. A number of technological applications have also been envisioned, in particular, chiral interconnect devices based on the high-Chern-number topological heterostructures [8].

Concerning current challenges of this field, we will discuss the issue of the Dirac point gap in the MnBi₂Te₄ topological surface state that caused a lot of controversy. While the early experimental measurements reported on large gaps, in agreement with ab initio calculations, a number of further studies claimed to observe a gapless dispersion of the MnBi₂Te₄ Dirac cone. A number of possible theoretical explanations of this unexpected behavior have been put forward, which we will discuss in the context of the available experimental data [9].

I acknowledge the support by MCIN/AEI/10.13039/501100011033/ (Grant PID2022-138210NB-I00) and ERDF A way of making Europe, by Ayuda CEX2023-001286-S financiada por MICIU/AEI/10.13039/501100011033, as well as MCIN with funding from European Union NextGenerationEU (PRTR-C17.I1) promoted by the Government of Aragon.

References:

[1] M.M. Otrokov et al. Nature 576, 16 (2019)

[2] M.M. Otrokov et al. Phys. Rev. Lett. 122, 07202 (2019)

[3] Y. Gong et al., Chin. Phys. Lett. 36, 076801 (2019)

[4] A.Y. Vyazovskaya, M. Bosnar, E.V. Chulkov, M.M. Otrokov. Commun Mater 6, 88 (2025). Review article

[5] I.I. Klimovskikh, M.M. Otrokov et al. npj Quantum Mater. 5, 54 (2020)

[6] Y. Deng et al. Science 367, 895 (2020)

[7] A. Gao et al. Nature 595, 521 (2021)

[8] M. Bosnar, A.Yu. Vyazovskaya, E.K. Petrov, E.V. Chulkov, M.M. Otrokov. npj 2D Mater. Appl. 7, 33 (2023)

[9] M. Garnica, M.M. Otrokov et al. npj Quantum Mater. 7, 7 (2022)