By Peter Weiss
Stare at atoms long enough and you may start seeing ghosts. That’s what physicists at an IBM laboratory discovered while peering at an ellipse of atoms they had built on a copper surface.
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Having used the probe of a scanning tunneling microscope (SN: 10/24/98, p. 268: https://www.sciencenews.org/sn_arc98/10_24_98/Bob2.htm) to maneuver 36 individual cobalt atoms into a corral, the researchers started to put additional cobalt atoms inside the ellipse as part of a magnetism experiment. After adding just one, however, they noticed something peculiar. The microscope signal intensified elsewhere in the ellipse as if a second atom were present, but none was.