Systematics of electronic and magnetic properties in the transition metal doped Sb2Te3 quantum anomalous Hall platform

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 calculations with complementary experimental techniques, i.e., scanning tunneling microscopy, resonant photoemission, and x-ray magnetic circular dichroism, 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 topological insulators. 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.

Magnetic-impurity-induced modifications to ultrafast carrier dynamics in the ferromagnetic topological insulators Sb2−xVxTe3

“…The observed Sb 5p magnetic moment at the non-magnetic element is most likely induced by the V magnetic dopant. This result is in good agreement with the previous XMCD studies for Cr-or V-doped compounds [29,33,35,36,38]. More importantly, very small but clear XMCD signals are observed at the Te M 4,5 absorption edges.…”

“…The microscopic origin of the ferromagnetism and the QAH state has been extensively investigated by theoretical and experimental approaches [26][27][28][29][30][31][32][33][34][35][36][37][38]. Element-specific x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) experiments revealed that the long-range ferromagnetic order in the magnetic TIs is caused by a magnetic coupling between p-d electrons of the host and magnetic dopants because the clear XMCD signals were observed not only at V (Cr) sites but also at Sb sites [29,33,35,36,38]. In addition, first principles calculations, scanning tunneling microscopy/spectroscopy (STM/STS) and resonant photoemission spectroscopy identified the impurity states of vanadium dopants at or near the Dirac node [26,30,32,36].…”

“…Element-specific x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) experiments revealed that the long-range ferromagnetic order in the magnetic TIs is caused by a magnetic coupling between p-d electrons of the host and magnetic dopants because the clear XMCD signals were observed not only at V (Cr) sites but also at Sb sites [29,33,35,36,38]. In addition, first principles calculations, scanning tunneling microscopy/spectroscopy (STM/STS) and resonant photoemission spectroscopy identified the impurity states of vanadium dopants at or near the Dirac node [26,30,32,36]. These might induce several modifications to the band structure [39][40][41], implying, for instance, the existence of a mobility gap, namely, the coexistence of the gap opening and the presence of impurity states at the Dirac node [30].…”

Connection topology of step edge state bands at the surface of a three dimensional topological insulator

“…Taken together, this large upward rescaling of the U-axis, as well as the non-infinite critical potential for changing the Dirac point connection topology ¹ ¥ ( ) U C , and the appearance of successive Dirac-connected states as a function of U, reveal that including 3D structure and coupling with bulk band symmetries can have an important role in defining the edge state properties. This finding is consistent with other recent literature suggesting that impurity state LDOS may include a significant bulk band component at a TI surface [14,26,39,40]. However, the rescaled 2D CL model can do an excellent job for edge states with group velocities not far removed from their band of origin (the lower or upper Dirac cone), and accurately describes the low-momentum dispersion for over half of the parameter space explored in figure 4(e).…”

Ab initio investigation of impurity-induced in-gap states in Bi2Te3 and Bi2Se3

“…We point out that the impurityinduced in-gap states are strongly localized in the vicinity of the impurities, so that at larger distances the magnetic proximity effect could still lead to a gap in density of states (of the surface state). This could support a quantum anomalous Hall state [31,47,48].…”