Quiet times in iron-walled quantum corrals - research into standing-wave patterns generated by electron waves bouncing within quantum corrals or similar enclosed structures - Brief Article

Science News, June 18, 1994 by Ivars Peterson

A stone tossed into a placid pool generates ripples, which spread out in concentric rings and rebound from the pool's rim and from any obstructions breaking the water's surface. These disturbances overlap to create complex interference patterns.

Electrons confined to small spaces act like waves and produce similar patterns when scattered by impurities and edges on a crystal surface (SN: 5/21/94, p.327) or reflected by "walls" of atoms (SN: 10/9/93, p.228). The resulting standing-wave patterns can be observed with a scanning tunneling microscope.

Now, researchers have worked out a way of predicting with great accuracy the standing-wave patterns produced by electron waves bouncing around inside enclosed structures, or quantum corrals, of particular shapes. The theory also indicates that certain types of atomic walls readily absorb electron waves, reducing reflections.

Eric J. Heller of Harvard University, Michael E Crommie of Boston University, and Christopher P. Lutz and Donald M. Eigler of the IBM Almaden Research Center in San Jose, Calif., describe their findings in the June 9 NATURE.

To test their theory the researchers computed the standing-wave pattern that would result from electron motion within a stadium-shaped enclosure. They compared the results with the behavior of surface electrons within a quantum corral created by placing 76 iron atoms in an elongated-ring formation on a copper crystal surface.

"The theory gives excellent agreement with the experiment," the team concludes.

The calculations also reveal that the iron atoms soak up a large proportion of the electron waves that impinge on them. This suggests that electrons are shunted from the surface via iron atoms into the copper crystal.

"In an acoustic analogy, the corral is therefore a rather quiet chamber," the researchers say.

This absorption of electron waves limits the usefulness of such nanostructures for studying various quantum effects. However, it may be possible to make highly reflective walls by building these structures on extremely thin layers of material instead of on thick copper crystals.