Science 327, 843–846 (2010)

The wave-like nature of matter leads to interference patterns similar to those on the surface of a pond. This was famously demonstrated in 1993 by Don Eigler and colleagues at IBM, who used a scanning tunnelling microscope (STM) to image the ripples of electrons confined inside a ring of iron atoms. Now, Valery Stepanyuk, Dirk Sander and colleagues at the Max Planck Institute of Microstructure Physics have imaged the spatial modulation of electron-spin polarization caused by electron interference patterns inside a single nanostructure.

Building on previous work, the researchers used a spin-polarized STM to probe a single triangular island of cobalt that was 12 nm long and supported on a copper substrate. The current flowing from the STM tip depended on its magnetic orientation relative to the part of the island just below it, and was used to construct a spatial map of polarization across the island. This map turned out to be a pattern of dots in the interior of the island, and a single rim state around its edge.

The pattern originated from the confinement of electrons inside the nanostructure, which led to spin-dependent interference patterns. This method may be applied to imaging spin polarization in other nanostructures. Furthermore, the interference patterns were shown to depend on the energy of the electrons, indicating a possible route to controlling polarization.