Temperature dependence of a single Kondo impurity.

Recent advances in scanning tunneling microscopy have allowed the observation of the Kondo effect for individual magnetic atoms. One hallmark of the Kondo effect is a strong temperature-induced broadening of the Kondo resonance. In order to test this prediction for individual impurities, we have investigated the temperature dependent electronic structure of isolated Ti atoms on Ag(100). We find that the Kondo resonance is strongly broadened in the temperature range T = 6.8 K to T = 49.0 K. These results are in good agreement with theoretical predictions for Kondo impurities in the Fermi liquid regime, and confirm the role of electron-electron scattering as the main thermal broadening mechanism.

Kondo response of a single antiferromagnetic chromium trimer.

The triangular Cr trimer (Cr(3)) is a fundamental component in a number of frustrated, antiferromagnetic systems. We have used atomic manipulation and scanning tunneling spectroscopy to probe the local behavior of this basic magnetic substructure by fabricating and analyzing individual Cr trimers at the surface of gold. We find that Cr trimers can be reversibly switched between two distinct electronic states. This phenomenon can be explained as the Kondo response of a spin-switching, magnetically frustrated nanocluster. Such behavior is consistent with noncollinear magnetic states predicted for Cr trimers whose structures differ by the position of a single atom.

Tunneling into a single magnetic atom: spectroscopic evidence of the kondo resonance

The Kondo effect arises from the quantum mechanical interplay between the electrons of a host metal and a magnetic impurity and is predicted to result in local charge and spin variations around the magnetic impurity. A cryogenic scanning tunneling microscope was used to spatially resolve the electronic properties of individual magnetic atoms displaying the Kondo effect. Spectroscopic measurements performed on individual cobalt atoms on the surface of gold show an energetically narrow feature that is identified as the Kondo resonance-the predicted response of a Kondo impurity. Unexpected structure in the Kondo resonance is shown to arise from quantum mechanical interference between the d orbital and conduction electron channels for an electron tunneling into a magnetic atom in a metallic host.