Electrical detection of surface spin polarization of candidate topological Kondo insulator SmB6

TL;DR

This study provides electrical evidence of spin polarization in the surface states of SmB6, supporting its classification as a topological Kondo insulator with spin helical surface states, and explores the temperature-dependent surface-bulk conduction crossover.

Contribution

It demonstrates direct electrical detection of surface spin polarization in SmB6, confirming the presence of metallic spin helical surface states in this topological Kondo insulator.

Findings

Surface spin voltage proportional to spin polarization and current direction.

Lower bound of surface spin polarization estimated at 15%.

Spin polarization strongly temperature dependent due to surface-bulk crossover.

Abstract

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 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 15 percent based on the quantum transport model providing direct evidence that SmB6 supports metallic spin helical surface states.