Recent Advances in Physics and Materials Science of Magnetic Topological Insulators

Topological insulators (TIs) are narrow–gap semiconductors characterized by the gapless Dirac-like surface state and protected by time-reversal (TR) symmetry. Two-dimensional TIs or quantum spin Hall insulators (QSHIs) are realized in thin film insulators and possess this state at the film edge where spin transport can be effectuated. Introduction of a magnetic field (external or internal) breaks TR symmetry and causes splitting of the topological surface state at the Dirac point thus making the surface insulating. These ferromagnetic TIs realize quantum anomalous Hall effect (QAHE) in two-dimensional systems. Internal magnetic field in TIs can be created in various ways, in particular, by introducing vacancies or carbon atoms [1], doping with 3d-transition metal atoms [2], displaying magnetic semiconductors or organic overlayers as well as bulk materials on the surface of threeor two-dimensional TIs [3-5]. Magnetic field effect on the TI surface state (SS) can be also realized due to extension of the TI SS into the magnetic overlayer [6-9]. Antiferromagnetic TIs can realize such intriguing effects as magnetoelectric effect [10] and axion insulator phase [11]. Here I present and discuss recent results of the study of nonmagnetic, ferro-, and antiferro-magnetic topological insulators and heterostructures. New method for engineering of heterostructures that results systematically in a big splitting of the Dirac cone [6-9,12-14] is discussed and new perspectives for realizations of exotic topological phases are outlined. [1] S.Roy et al., Phys. Rev. Lett. 113 (2014) 116802. [2] J.Henk et al., Phys. Rev. Lett. 109 (2012) 076801. [3] V.N.Men'shov et al. Phys. Rev. B 88 (2013) 224401. [4] M.M.Otrokov, E.V.Chulkov, and A.Arnau, Phys. Rev. B 92 (2015) 165309. [5] S.V.Eremeev et al., (2013), Phys. Rev. B 88 (2013) 144430. [6] T.Hirahara et al., Nano Letters, 17, 3493 (2017). [7] M.M.Otrokov et al., JETP Lett. 105, 297 (2017). [8] M.M.Otrokov et al., 2D Materials, 4, 025082 (2017). [9] S.V.Eremeev, M.M.Otrokov, and E.V.Chulkov, Nano Letters, 18, 6521 (2018). [10] R.S.K.Mong, A.M.Essin, and J.E.Moore, Phys. Rev. B 81 (2010) 245209. [11] J.Wang, B.Lian, and S.-C.Zhang, Phys. Rev. B 93 (2016) 045115. [12] E.K.Petrov et al., JETP Lett. 109, 121 (2019). [13] M.M.Otrokov et al., Phys. Rev. Lett. 122, 107202 (2019). [14] M.M.Otrokov et al., will be published by Nature, December 19 (2019).