Negative Te spin polarization responsible for ferromagnetic order in the doped topological insulator V(SbBi)Te

トポロジカル絶縁体V(SbBi)Teの強磁性の起源

Ye, M.*; Xu, T.*; Li, G.*; Qiao, S.*; 竹田 幸治   ; 斎藤 祐児  ; Zhu, S.-Y.*; Nurmamat, M.*; 角田 一樹*; 石田 行章*; Shin, S.*; 木村 昭夫*

Ye, M.*; Xu, T.*; Li, G.*; Qiao, S.*; Takeda, Yukiharu; Saito, Yuji; Zhu, S.-Y.*; Nurmamat, M.*; Sumida, Kazuki*; Ishida, Yukiaki*; Shin, S.*; Kimura, Akio*

We investigate the microscopic origin of ferromagnetism coupled with topological insulators in V-doped (Sb,Bi)Te employing X-ray magnetic circular dichroism and angle-resolved two-photon photoemission spectroscopies, combined with first-principles calculations. We found an magnetic moment at the Te site anti-parallel to that of the V and Sb sites, which plays a key role in the ferromagnetic order. We ascribe it to the hybridization between Te 5 and V 3 majority spin states at the Fermi energy, consistent with the Zener-type - exchange interaction scenario. The substitution of Bi for Sb suppresses the bulk ferromagnetism by introducing extra electron carriers in the majority spin channel of the Te states that compensates the antiparallel magnetic moment on the Te site. Our findings reveal important clues to designing magnetic topological insulators with higher Curie temperature that work under ambient conditions.