Bulk Kondo Effect studied by STM
Mapping Itinerant Electrons around Kondo Impurities
[Phys. Rev. Lett. 108, 166604 (2012)]
We investigate single Fe and Co atoms buried below a Cu(100) surface using low temperature scanning tunneling spectroscopy. By mapping the local density of states of the itinerant electrons at the surface, the Kondo resonance near the Fermi energy is analyzed. Probing bulk impurities in this well-defined scattering geometry allows separating the physics of the Kondo system and the measuring process. The line shape of the Kondo signature shows an oscillatory behavior as a function of depth of the impurity as well as a function of lateral distance. The oscillation period along the different directions reveals that the spectral function of the itinerant electrons is anisotropic.
Long-range Kondo signature of a single magnetic impurity
[Nature Physics 10.1038/nphys1876 (2011)]
The Kondo effect, one of the first recognized correlation phenomena in condensed matter physics1, has regained attention because of scanning tunnelling spectroscopy (STS) experiments performed on single magnetic impurities. Despite the sub-nanometre resolution capability of local probe techniques, one of the fundamental aspects of Kondo physics, its spatial extension, is still subject to discussion. Until now all STS studies on single adsorbed atoms have shown that observable Kondo features vanish rapidly with increasing distance from the impurity4–9. Here we report on a hitherto unobserved long-range Kondo signature for single magnetic atoms of Fe and Co buried under a Cu(100) surface. We present a theoretical interpretation of the measured signatures using a combined approach of band structure and many body numerical renormalization group (NRG) calculations. These are in excellent agreement with the rich spatially and spectroscopically resolved experimental data.
In collaboration with:
T. Pruschke, Piet Dargel and R. Peters, Institut fürr Theoretische Physik, Georg-August-Universit Göttingen, Germany
Kondo resonance of single Co atoms embedded in Cu(111)
[Phys. Rev. B 69,201103(R) (2004)]
The Kondo resonance of single Co atoms embedded in a Cu matrix has been investigated with tunnelling spectroscopy at T = 8 K. Dilute magnetic alloys were prepared by homoepitaxial growth of Cu(111) films incorporating approximately 0.1% Co atoms as magnetic scattering centers. The Co impurities in the first layer of the Cu matrix show a characteristic, symmetric dip in the differential conductance around zero bias, indicating the presence of the many-body Abrikosov-Suhl resonance. The corresponding Kondo temperature is found to be TK~ 405, which is much higher than previously reported values for Co adsorbate atoms.
In collaboration with:
K. Schönhammer, Institut fürr Theoretische Physik, Georg-August-Universit Göttingen, Germany
Our work (Göttingen) is supported by the Deutsche Forschungsgemeinschaft (DFG) within SFB 602 (TP A3)