bNMR reveals nanoscale surface details in topological insulators:
Wolfgang Pauli said, “God made the bulk; surfaces were invented by the devil”, a recognition of the fact that theories and experimental measurements of near-surface properties are very difficult. Surfaces may be difficult to study, but it is where much interesting physics arise.
Topological insulators (TI) are materials where the bulk is an insulator but whose surface contains conducting states, which means that electrons can only move along the surface of the material. Topologically protected states could act as a source of spin-polarized electrons with properties relevant to spintronics applications including quantum computing. As published in the Proceedings of the National Academy of Sciences (2015) researchers at CMMS used bNMR spectroscopy as a nano-scale depth-resolved probe of magnetism and conductivity within about 10 nm of the free surface of (Bi,Sb)2Te3. This depth-dependent study of electronic and magnetic properties of TI epitaxial layers using implanted, spbin-polarized 8Li+ ions reveals differences in the band structure between the near-surface and deeper into the bulk material.