Nature of the Dirac gap modulation and surface magnetic interaction in axion antiferromagnetic topological insulator MnBi$_2$Te$_4$
/ Authors
A. Shikin, D. Estyunin, I. Klimovskikh, S. Filnov, E. Schwier, S. Kumar, K. Myamoto, T. Okuda, A. Kimura, K. Kuroda
and 11 more authors
K. Yaji, S. Shin, Y. Takeda, Y. Saitoh, Z. Aliev, N. Mamedov, I. Amiraslanov, M. Babanly, M. Otrokov, S. Eremeev, E. Chulkov
/ Abstract
Modification of the gap at the Dirac point (DP) in antiferromagnetic (AFM) axion topological insulator MnBi$_2$Te$_4$ and its electronic and spin structure has been studied by angle- and spin-resolved photoemission spectroscopy (ARPES) under laser excitation with variation of temperature (9-35~K), light polarization and photon energy. We have distinguished both a large (62-67~meV) and a reduced (15-18~meV) gap at the DP in the ARPES dispersions, which remains open above the Neel temperature ($T_\mathrm{N}=24.5$~K). We propose that the gap above $T_\mathrm{N}$ remains open due to short-range magnetic field generated by chiral spin fluctuations. Spin-resolved ARPES, XMCD and circular dichroism ARPES measurements show a surface ferromagnetic ordering for large-gap sample and significantly reduced effective magnetic moment for the reduced-gap sample. These effects can be associated with a shift of the topological DC state towards the second Mn layer due to structural defects and mechanical disturbance, where it is influenced by a compensated effect of opposite magnetic moments.
Journal: arXiv: Materials Science