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

Abstract

We combine low energy muon spin rotation (LE-$\mu$SR) and soft-X-ray angle-resolved photoemission spectroscopy (SX-ARPES) to study the magnetic and electronic properties of magnetically doped topological insulators, (Bi,Sb)${}_2$Te${}_3$. We find that one achieves a full magnetic volume fraction in samples of (V/Cr)${}_x$(Bi,Sb)${}_{2-x}$Te${}_3$ at doping levels x $\gtrsim$ 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 $L_3$ 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.

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• Quantized Anomalous Hall Effect in Magnetic Topological Insulators
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• Intertwined magnetic, structural, and electronic transitions in V${}_2$O${}_3$