Spectroscopic perspective on the interplay between electronic and magnetic properties of magnetically doped topological insulators

Abstract

We combine low energy muon spin rotation (LE-μSR) and soft-x-ray angle-resolved photoemission spectroscopy (SX-ARPES) to study the magnetic and electronic properties of magnetically doped topological insulators, (Bi,Sb)2Te3. We find that one achieves a full magnetic volume fraction in samples of (V/Cr)x(Bi,Sb)2-xTe3 at doping levels x=0.16. The observed magnetic transition is not sharp in temperature indicating a gradual magnetic ordering. We find that the evolution of magnetic ordering is consistent with formation of ferromagnetic islands which increase in number and/or volume with decreasing temperature. Resonant ARPES at the V L3 edge reveals a nondispersing impurity band close to the Fermi level as well as V weight integrated into the host band structure. Calculations within the coherent potential approximation of the V contribution to the spectral function confirm that this impurity band is caused by V in substitutional sites. The implications of our results on the observation of the quantum anomalous Hall effect at mK temperatures are discussed.The work at PSI was supported by the Swiss National Science Foundation (SNF-Grant No. 200021_165910). We acknowledge support from DFG through priority program SPP1666 (Topological Insulators), University of the Basque Country (Grants No. GIC07IT36607 and No. IT-756-13), Spanish Ministry of Science and Innovation (Grants No. FIS2013-48286-C02-02-P, No. FIS2013-48286-C02-01-P, and No. FIS2016-75862-P) and Tomsk State University competitiveness improvement programme (Project No. 8.1.01.2017). Partial support by the Saint Petersburg State University Project No. 15.61.202.2015 is also acknowledged. At MIT, C.Z.C. and J.S.M. acknowledge support from the STC Center for Integrated Quantum Materials under NSF grant DMR-1231319 as well as grants NSF (DMR-1207469, DMR1700137), ONR (N00014-13-1-0301 and N00014-16-1-2657). C.Z.C also acknowledges the support from the startup grant provided by Penn State University.Peer Reviewe