The Kondo insulator compound SmB6 has emerged as a strong candidate for the realization of a topologically nontrivial state in a strongly correlated system, a topological Kondo insulator, which can be a novel platform for investigating the interplay between nontrivial topology and emergent correlation-driven phenomena in solid-state systems. Electronic transport measurements on this material, however, so far showed only the robust surface-dominated charge conduction at low temperatures, lacking evidence of its connection to the topological nature by showing, for example, spin polarization due to spin-momentum locking. Here, we find evidence for surface-state spin polarization by electrical detection of a current-induced spin chemical-potential difference on the surface of a SmB6 single crystal. We clearly observe that a surface-dominated spin voltage, which is proportional to the projection of the spin polarization onto the contact magnetization, is determined by the direction and magnitude of the charge current and is strongly temperature dependent due to the crossover from surface to bulk conduction. We estimate the lower bound of the surface-state net spin polarization as 25% based on the quantum transport model, providing direct evidence that SmB6 supports metallic spin helical surface states.
Bibliographical noteFunding Information:
This research was supported by the Basic Science Research Program (Grants No. NRF-2015R1C1A1A02037430 and No. 2018R1A2A3075438), Priority Research Centers Program (Grant No. 2015R1A5A1037668) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning, Research Resettlement Fund for the new faculty of Seoul National University, and Creative-Pioneering Researchers Program through Seoul National University. H.C. and J.L. were supported by National Research Foundation of Korea (NRF) through the government of Korea (Grant No. NRF-2018R1A2A1A05079060) and Creative Materials Discovery Program (Grant No. 2017M3D1A1040828). Preparation of Sm B 6 material was funded by AFOSR (Grant No. FA9550-14-1-0332) and by the Gordon and Betty Moore Foundations EPiQS Initiative through Grant No. GBMF4419. Electrical measurements used shared facilities funded by the KIST institutional program and the National Research Council of Science and Technology (Grant No. CAP-16-01-KIST).
© 2019 American Physical Society.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics