Rare earth ions typically exhibit larger magnetic moments than transition metal ions and thus promise the opening of a wider exchange gap in the Dirac surface states of topological insulators. Yet, in a recent photoemission study of Eu-doped Bi2Te3 films, the spectra remained gapless down to T=20K. Here, we scrutinize whether the conditions for a substantial gap formation in this system are present by combining spectroscopic and bulk characterization methods with theoretical calculations. For all studied Eu doping concentrations, our atomic multiplet analysis of the M4,5 x-ray absorption and magnetic circular dichroism spectra reveals a Eu2+ valence and confirms a large magnetic moment, consistent with a 4f78S7/2 ground state. At temperatures below 10K, bulk magnetometry indicates the onset of antiferromagnetic (AFM) ordering. This is in good agreement with density functional theory, which predicts AFM interactions between the Eu impurities. Our results support the notion that antiferromagnetism can coexist with topological surface states in rare-earth doped Bi2Te3 and call for spectroscopic studies in the kelvin range to look for novel quantum phenomena such as the quantum anomalous Hall effect.
@article{arxiv.2009.11733,
title = {Incipient antiferromagnetism in the Eu-doped topological insulator Bi$_2$Te$_3$},
author = {Abdul Tcakaev and Volodymyr B. Zabolotnyy and Celso I. Fornari and Philipp Rüßmann and Thiago R. F. Peixoto and Fabian Stier and Michael Dettbarn and Philipp Kagerer and Eugen Weschke and Enrico Schierle and Peter Bencok and Paulo H. O. Rappl and Eduardo Abramof and Hendrik Bentmann and Eberhard Goering and Friedrich Reinert and Vladimir Hinkov},
journal= {arXiv preprint arXiv:2009.11733},
year = {2020}
}