Evolution of Dopant-Concentration-Induced Magnetic Exchange Interaction in Topological Insulator Thin Films

To date, the quantum anomalous Hall effect has been realized in chromium (Cr)-and/or vanadium(V)-doped topological insulator (Bi,Sb)2Te3 thin films. In this work, we use molecular beam epitaxy to synthesize both V-and Cr-doped Bi2Te3 thin films with controlled dopant concentration. By performing magneto-transport measurements, we find that both systems show an unusual yet similar ferromagnetic response with respect to magnetic dopant concentration; specifically the Curie temperature does not increase monotonically but shows a local maximum at a critical dopant concentration. We attribute this unusual ferromag-netic response observed in Cr/V-doped Bi2Te3 thin films to the dopant-concentration-induced magnetic exchange interaction, which displays evolution from van Vleck-type ferromagnetism in a nontrivial magnetic topological insulator to Ruderman-Kittel-Kasuya-Yosida (RKKY)-type ferromagnetism in a trivial diluted magnetic semiconductor. Our work provides insights into the ferromagnetic properties of magnetically doped topological insulator thin films and facilitates the pursuit of high-temperature quantum anomalous Hall effect.

Automated summary

In this study, we synthesized doped Bi2Te3 thin films with controlled doping concentrations using molecular beam epitaxy. By conducting magneto-transport measurements, we observed an unusual ferromagnetic response in both chromium (Cr)- and vanadium (V)-doped films, where the Curie temperature shows a local maximum at a critical doping concentration. We attribute this behavior to the dopant-concentration-induced magnetic exchange interaction, which transforms the ferromagnetism from van Vleck-type in a nontrivial magnetic topological insulator to Ruderman-Kittel-Kasuya-Yosida (RKKY)-type in a trivial diluted magnetic semiconductor. This work provides insights into the ferromagnetic properties of magnetically doped topological insulator thin films and facilitates the exploration of high-temperature quantum anomalous Hall effect.