Mogi Masataka, Kawamura Minoru, Tsukazaki Atsushi, Yoshimi Ryutaro, Takahashi Kei S, Kawasaki Masashi, Tokura Yoshinori
Department of Applied Physics and Quantum Phase Electronics Center, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan.
RIKEN Center for Emergent Matter Science, Wako, Saitama 351-0198, Japan.
Sci Adv. 2017 Oct 6;3(10):eaao1669. doi: 10.1126/sciadv.aao1669. eCollection 2017 Oct.
Exploration of novel electromagnetic phenomena is a subject of great interest in topological quantum materials. One of the unprecedented effects to be experimentally verified is the topological magnetoelectric (TME) effect originating from an unusual coupling of electric and magnetic fields in materials. A magnetic heterostructure of topological insulator (TI) hosts such exotic magnetoelectric coupling and can be expected to realize the TME effect as an axion insulator. We designed a magnetic TI with a tricolor structure where a nonmagnetic layer of (Bi, Sb)Te is sandwiched by a soft ferromagnetic Cr-doped (Bi, Sb)Te and a hard ferromagnetic V-doped (Bi, Sb)Te. Accompanied by the quantum anomalous Hall (QAH) effect, we observe zero Hall conductivity plateaus, which are a hallmark of the axion insulator state, in a wide range of magnetic fields between the coercive fields of Cr- and V-doped layers. The resistance of the axion insulator state reaches as high as 10 ohms, leading to a gigantic magnetoresistance ratio exceeding 10,000,000% upon the transition from the QAH state. The tricolor structure of the TI may not only be an ideal arena for the topologically distinct phenomena but can also provide magnetoresistive applications for advancing dissipation-less topological electronics.
探索新型电磁现象是拓扑量子材料中一个备受关注的课题。有待通过实验验证的前所未有的效应之一是拓扑磁电（TME）效应，它源于材料中电场和磁场的异常耦合。拓扑绝缘体（TI）的磁性异质结构具有这种奇异的磁电耦合，有望作为轴子绝缘体实现TME效应。我们设计了一种具有三色结构的磁性TI，其中非磁性的（Bi，Sb）Te层夹在软铁磁Cr掺杂的（Bi，Sb）Te和硬铁磁V掺杂的（Bi，Sb）Te之间。伴随着量子反常霍尔（QAH）效应，我们在Cr掺杂层和V掺杂层的矫顽场之间的宽磁场范围内观察到零霍尔电导率平台，这是轴子绝缘体状态的一个标志。轴子绝缘体状态的电阻高达10欧姆，在从QAH状态转变时导致巨大的磁阻比超过10,000,000%。TI的三色结构不仅可能是拓扑不同现象的理想场所，还可以为推进无耗散拓扑电子学提供磁阻应用。
