Systematics of electronic and magnetic properties in the transition metal doped Sb$_2$Te$_3$ quantum anomalous Hall platform

TL;DR

This study systematically investigates how transition-metal doping affects the electronic and magnetic properties of Sb$_2$Te$_3$, revealing impurity-specific effects on topological surface states and magnetic anisotropy crucial for realizing the quantum anomalous Hall effect.

Contribution

It combines DFT calculations with experimental techniques to provide a comprehensive understanding of impurity effects in TM-doped Sb$_2$Te$_3$, guiding the realization of robust QAHE.

Findings

TM dopants alter electronic structure via impurity bands

Impurity type determines the impact on topological surface states

Magnetic anisotropy varies with impurity and affects gap stability

Abstract

The quantum anomalous Hall effect (QAHE) has recently been reported to emerge in magnetically-doped topological insulators. Although its general phenomenology is well established, the microscopic origin is far from being properly understood and controlled. Here we report on a detailed and systematic investigation of transition-metal (TM)-doped Sb$_2$Te$_3$. By combining density functional theory (DFT) calculations with complementary experimental techniques, i.e., scanning tunneling microscopy (STM), resonant photoemission (resPES), and x-ray magnetic circular dichroism (XMCD), we provide a complete spectroscopic characterization of both electronic and magnetic properties. Our results reveal that the TM dopants not only affect the magnetic state of the host material, but also significantly alter the electronic structure by generating impurity-derived energy bands. Our findings demonstrate the existence of a delicate interplay between electronic and magnetic properties in TM-doped TIs. In particular, we find that the fate of the topological surface states critically depends on the specific character of the TM impurity: while V- and Fe-doped Sb$_2$Te$_3$ display resonant impurity states in the vicinity of the Dirac point, Cr and Mn impurities leave the energy gap unaffected. The single-ion magnetic anisotropy energy and easy axis, which control the magnetic gap opening and its stability, are also found to be strongly TM impurity-dependent and can vary from in-plane to out-of-plane depending on the impurity and its distance from the surface. Overall, our results provide general guidelines for the realization of a robust QAHE in TM-doped Sb$_2$Te$_3$ in the ferromagnetic state.