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

TL;DR

This study combines advanced spectroscopic techniques to explore how magnetic doping influences the electronic and magnetic properties of topological insulators, revealing gradual magnetic ordering and impurity band formation relevant to quantum anomalous Hall effects.

Contribution

It provides new insights into the magnetic and electronic interplay in doped topological insulators using combined LE-μSR and SX-ARPES techniques, highlighting impurity band formation and magnetic inhomogeneity.

Findings

Full magnetic volume fraction achieved at doping levels x ≥ 0.16

Gradual magnetic transition indicating inhomogeneous magnetic ordering

Identification of impurity band near Fermi level caused by V substitution

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.