Electron paramagnetic resonance of individual atoms on a surface

EPR, one atom at a time Electron paramagnetic resonance (EPR) usually detects atoms with unpaired electrons as ensemble averages. Baumann et al. used a spin-polarized scanning tunneling microscope tip to measure EPR spectra of single iron atoms adsorbed on a magnesium oxide surface at cryogenic temperatures. The measurement depends on the atomic orbital symmetry; no signal was observed for cobalt atoms under the same conditions Science , this issue p. 417