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  • Letter
  • Open Access

Two-dimensional ferromagnetic extension of a topological insulator

P. Kagerer1,2, C. I. Fornari1,2,*, S. Buchberger1,2, T. Tschirner2,3, L. Veyrat2,3,4, M. Kamp5, A. V. Tcakaev2,4, V. Zabolotnyy2,4, S. L. Morelhão6 et al.

B. Geldiyev1,2, S. Müller1,2, A. Fedorov2,3,7, E. Rienks7, P. Gargiani8, M. Valvidares8, L. C. Folkers2,9, A. Isaeva3,10, B. Büchner2,3, V. Hinkov2,4, R. Claessen2,4, H. Bentmann1,2,†, and F. Reinert1,2

  • 1Physikalisches Institut (EP7), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
  • 2Würzburg-Dresden Cluster of Excellence ct.qmat, Germany
  • 3Leibniz IFW Dresden, Helmholtzstrasse 20, D-01069 Dresden, Germany
  • 4Physikalisches Institut (EP4), Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
  • 5Physikalisches Institut and Röntgen-Center for Complex Material Systems (RCCM), Fakultät für Physik und Astronomie, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany
  • 6Instituto de Física, Universidade de São Paulo, 05508-090 São Paulo, SP, Brazil
  • 7Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Strasse 15, D-12489 Berlin, Germany
  • 8ALBA Synchrotron Light Source, E-08290 Cerdanyola del Valles, Spain
  • 9Institut für Festkörper- und Materialphysik, Technische Universität Dresden, D-01062 Dresden, Germany
  • 10Van der Waals – Zeeman Institute, IoP, University of Amsterdam, NL-1098 XH Amsterdam, The Netherlands

  • *Celso.Fornari@physik.uni-wuerzburg.de
  • †Hendrik.Bentmann@ntnu.no; Present address: Center for Quantum Spintronics, Department of Physics, NTNU Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
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Phys. Rev. Research 5, L022019 – Published 1 May, 2023

DOI: https://doi.org/10.1103/PhysRevResearch.5.L022019

Abstract

Inducing a magnetic gap at the Dirac point of the topological surface state (TSS) in a three-dimensional (3D) topological insulator (TI) is a route to dissipationless charge and spin currents. Ideally, magnetic order is present only at the surface, as through proximity of a ferromagnetic (FM) layer. However, experimental evidence of such a proximity-induced Dirac mass gap is missing, likely due to an insufficient overlap of TSS and the FM subsystem. Here, we take a different approach, namely ferromagnetic extension (FME), 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. Ferromagnetic extension paves the way to explore the interplay of strictly 2D magnetism and topological surface states, providing perspectives for realizing robust quantum anomalous Hall and chiral Majorana states.

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Phys. Rev. Research 5, L022019– Published 1 May, 2023
  • Received 2 June 2022
  • Revised 9 September 2022
  • Accepted 9 February 2023
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

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