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arXiv · 2207.14421

Two-dimensional ferromagnetic extension of a topological insulator

P. Kagerer·C. I. Fornari·S. Buchberger·T. Tschirner·L. Veyrat·M. Kamp·A. V. Tcakaev·V. Zabolotnyy·S. L. Morelhão·B. Geldiyev·S. Müller·A. Fedorov·E. Rienks·P. Gargiani·M. Valvidares·L. C. Folkers·A. Isaeva·B. Büchner·V. Hinkov·R. Claessen·H. Bentmann·F. Reinert
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Abstract

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 Bi$_2$Te$_3$, interfaced with a monolayer of the lattice-matched van der Waals ferromagnet MnBi$_2$Te$_4$. Robust 2D ferromagnetism with out-of-plane anisotropy and a critical temperature of $\text{T}_\text{c}\approx$~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 T$_c$. 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.

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P. Kagerer, C. I. Fornari, S. Buchberger, T. Tschirner, L. Veyrat, M. Kamp, A. V. Tcakaev, V. Zabolotnyy, S. L. Morelhão, B. Geldiyev, S. Müller, A. Fedorov, E. Rienks, P. Gargiani, M. Valvidares, L. C. Folkers, A. Isaeva, B. Büchner, V. Hinkov, R. Claessen, H. Bentmann, F. Reinert. 2022-07-29. Two-dimensional ferromagnetic extension of a topological insulator. https://doi.org/10.1103/physrevresearch.5.l022019

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