The coherent transport of charge and spin is a key requirement of future devices for quantum computing and communication. Scattering at defects or impurities may significantly reduce the coherence of quantum-mechanical states, thereby affecting the device functionality. While numerous methods exist to experimentally assess charge transport, the real-space detection of a material’s ballistic spin transport properties with nanometer resolution remains a challenge.
In a novel experimental approach Patrick Härtl and Dr. Markus Leisegang combined for the first time spin-polarized scanning tunneling microscopy (SP-STM) and the recently introduced molecular nanoprobe (MONA) to SP-MONA. Hereby, spin-polarized charge carriers are injected with atomic precision from a magnetic STM tip and subsequently detected by a single surface-deposited phthalocyanine molecule via reversible electron-induced tautomerization events. The measurements were conducted on the BiAg2 surface alloy, which hosts an unconventinal Rasbha-split surface band. The results prove that charge carriers with up or down spin propagate in opposite directions, defined by the spin-momentum-locking of BiAg2. In future experiments, the novel SP-MONA technique will allow the investigation of transport in two-dimensional (2D) materials like graphene, bismuthene, or transition metal chalcogenides.
The results have been published in Nano Lett. 23, 11608 (2023).