Nanowires of Topological Kondo Insulators as Conduits for Spin-Polarized Tunneling Currents

The spin-momentum locked, symmetry protected surface or edge states of topological insulators are predicted to carry spin-polarized currents with a high degree of spin-polarization, which have a multitude of potential uses in spintronics, quantum computation and quantum communication applications. Achieving these in experiments have been challenging with garden-variety topological insulators due to the coexistence of highly conducting bulk states and the topological surface states (TSS) being buried deep in the bulk bands. However, topological Kondo insulators are pertinent for such studies as the TSS are well isolated from the bulk by the Kondo hybridization gap and are usually pinned at the Fermi energy. Here we design and implement a unique tunneling geometry to harness the spin-polarized TSS currents of the topological Kondo insulator, SmB₆. Using state-of-the-art nanofabrication techniques, we attach SmB₆ nanowires to the end of scanning tunneling microscope tips, effectively making a functional probe with atomic resolution. STM images with these nanowire tips reveal the static antiferromagnetic order in a canonical antiferromagnet indicating spin-selective tunneling from the nanowire. The antiferromagnetic order becomes invisible above 10 K (far below the Neel temperature), together with the suppression of the TSS. We further confirm a smoking gun signature of topological spin-polarized currents by imaging the contrast reversal of the antiferromagnetic order at opposite bias voltages. Our findings initiate a novel STM-based spectroscopy to both measure and utilize the unique electronic properties of topological materials.