Impurity states in the magnetic topological insulator V:(Bi,Sb)$_2$Te$_3$

TL;DR

This study investigates the electronic structure of V:(Bi,Sb)$_2$Te$_3$, a magnetic topological insulator, revealing impurity states that likely influence its ferromagnetism and quantum anomalous Hall effect.

Contribution

It provides the first element-specific analysis of V 3d impurity states and combines experimental and theoretical methods to elucidate their role in ferromagnetism.

Findings

V 3d impurity band exhibits high density of states near Fermi level

Experimental results supported by first-principles calculations

Impurity band contributes to ferromagnetism through multiple mechanisms

Abstract

The ferromagnetic topological insulator V:(Bi,Sb)$_2$Te$_3$ has been recently reported as a quantum anomalous Hall (QAH) system. Yet the microscopic origins of the QAH effect and the ferromagnetism remain unclear. One key aspect is the contribution of the V atoms to the electronic structure. Here the valence band of V:(Bi,Sb)$_2$Te$_3$ thin films was probed in an element-specific way by resonant photoemission spectroscopy. The signature of the V $3d$ impurity band was extracted, and exhibits a high density of states near Fermi level. First-principles calculations support the experimental results and indicate the coexistence of ferromagnetic superexchange and double exchange interactions. The observed impurity band is thus expected to contribute to the ferromagnetism via the interplay of different mechanisms.