Inducing a magnetic gap at the Dirac point of the topological surface state (TSS) in a 3D topological insulator (TI) is a route to dissipationless charge and spin currents. Ideally, magnetic order is present only at the surface and not in the bulk, e.g. through proximity of a ferromagnetic (FM) layer. However, such a proximity-induced Dirac mass gap has not been observed, likely due to insufficient overlap of TSS and the FM subsystem. Here, we take a different approach, namely FM extension, using a thin film of the 3D TI Bi2Te3, interfaced with a monolayer of the lattice-matched van der Waals ferromagnet MnBi2Te4. Robust 2D ferromagnetism with out-of-plane anisotropy and a critical temperature of Tc≈~15 K is demonstrated by X-ray magnetic dichroism and electrical transport measurements. Using angle-resolved photoelectron spectroscopy, we observe the opening of a sizable magnetic gap in the 2D FM phase, while the surface remains gapless in the paramagnetic phase above Tc. This sizable gap indicates a relocation of the TSS to the FM ordered Mn moments near the surface, which leads to a large mutual overlap.
@article{arxiv.2207.14421,
title = {Two-dimensional ferromagnetic extension of a topological insulator},
author = {P. Kagerer and C. I. Fornari and S. Buchberger and T. Tschirner and L. Veyrat and M. Kamp and A. V. Tcakaev and V. Zabolotnyy and S. L. Morelhão and B. Geldiyev and S. Müller and A. Fedorov and E. Rienks and P. Gargiani and M. Valvidares and L. C. Folkers and A. Isaeva and B. Büchner and V. Hinkov and R. Claessen and H. Bentmann and F. Reinert},
journal= {arXiv preprint arXiv:2207.14421},
year = {2023}
}