For quantum electronics, the possibility to finely tune the properties of magnetic topological insulators (TIs) is a key issue. We studied solid solutions between two isostructural Z2 TIs, magnetic MnBi2Te4 and nonmagnetic GeBi2Te4, with Z2 invariants of 1;000 and 1;001, respectively. For high-quality, large mixed crystals of GexMn1−xBi2Te4, we observed linear x-dependent magnetic properties, composition-independent pairwise exchange interactions along with an easy magnetization axis. The bulk band gap gradually decreases to zero for x from 0 to 0.4, before reopening for x>0.6, evidencing topological phase transitions (TPTs) between topologically nontrivial phases and the semimetal state. The TPTs are driven purely by the variation of orbital contributions. By tracing the x-dependent 6p contribution to the states near the fundamental gap, the effective spin-orbit coupling variation is extracted. As x varies, the maximum of this contribution switches from the valence to the conduction band, thereby driving two TPTs. The gapless state observed at x=0.42 closely resembles a Dirac semimetal above the Neel temperature and shows a magnetic gap below, which is clearly visible in raw photoemission data. The observed behavior of the GexMn1−xBi2Te4 system thereby demonstrates an ability to precisely control topological and magnetic properties of TIs.
@article{arxiv.2306.13024,
title = {Magnetic Dirac semimetal state of (Mn,Ge)Bi$_2$Te$_4$},
author = {Alexander S. Frolov and Dmitry Yu. Usachov and Artem V. Tarasov and Alexander V. Fedorov and Kirill A. Bokai and Ilya Klimovskikh and Vasily S. Stolyarov and Anton I. Sergeev and Alexander N. Lavrov and Vladimir A. Golyashov and Oleg E. Tereshchenko and Giovanni Di Santo and Luca Petaccia and Oliver J. Clark and Jaime Sanchez-Barriga and Lada V. Yashina},
journal= {arXiv preprint arXiv:2306.13024},
year = {2023}
}