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Instruments / Technical Area	Publication Details	Published	Actions
I10-Beamline for Advanced Dichroism - scattering	Incipient antiferromagnetism in the Eu-doped topological insulator Bi2Te3 A. Tcakaev , V. B. Zabolotnyy , C. I. Fornari , P. Rüßmann , T. R. F. Peixoto , F. Stier , M. Dettbarn , P. Kagerer , E. Weschke , E. Schierle , P. Bencok , P. H. O. Rappl , E. Abramof , H. Bentmann , E. Goering , F. Reinert , V. Hinkov Physical Review B 102 DOI: 10.1103/PhysRevB.102.184401 Diamond Proposal Number(s): [19994] Show Abstract ▼ Abstract: 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 Bi 2 Te 3 films, the spectra remained gapless down to T = 20 K. 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 M 4 , 5 x-ray absorption and magnetic circular dichroism spectra reveals a Eu 2 + valence and confirms a large magnetic moment, consistent with a 4 f 7 8 S 7 / 2 ground state. At temperatures below 10 K, 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 Bi 2 Te 3 and call for spectroscopic studies in the Kelvin range to look for novel quantum phenomena such as the quantum anomalous Hall effect.	Nov 2020
I09-Surface and Interface Structural Analysis	Incorporation of europium in Bi2Te3 topological insulator epitaxial films Celso I. Fornari , Hendrik Bentmann , Sergio L. Morelhao , Thiago R. F. Peixoto , Paulo Rappl , Abdul Tcakaev , Volodymyr Zabolotnyy , Martin Kamp , Tien-Lin Lee , Chul-Hee Min , Philipp Kagerer , Raphael Vidal , Anna Isaeva , Michael Ruck , Vladimir Hinkov , Friedrich Reinert , Eduardo Abramof The Journal Of Physical Chemistry C DOI: 10.1021/acs.jpcc.0c05077 Show Abstract ▼ Abstract: In the field of topological materials, the interaction between band topology and magnetism remains a current frontier for the advance of new topological states and spintronic functionalities. Doping with rare-earth elements with large magnetic moment is a current approach to exploit the phenomenology of such interaction. However, dopant solubility into the main matrix plays a major role. In this sense, the present work is focused on elucidating how Eu incorporates into Bi2Te3 lattice as a function of doping. This work reports a systematic investigation of the structural and electronic properties of bismuth telluride epitaxial layers doped with Eu. Bi2Te3 films were grown by molecular beam epitaxy (MBE) on (111) BaF2 substrates with nominal Eu doping ranging from 0 % up to 9 %. X-ray diffraction (XRD) analysis and scanning transmission electron microscopy (TEM) reveal that Eu atoms enter substitutionally on Bi sites up to 4 % of Eu doping. In contrast, the 9 % Eu-doped sample contains epitaxially oriented nanoclusters of EuTe. X ray photoelectron (XPS) and absorption (XAS) spectroscopies show that Eu atoms enter into the Bi2Te3 crystal matrix in the divalent Eu2+ state for all Eu concentrations. Angle resolved photoemission (ARPES) experiments indicate that the topological surface state is preserved in the presence of the local magnetic moments introduced by the Eu impurities.	Jun 2020

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