Long-range Kondo signature of a single magnetic impurity

The Kondo effect, one of the first recognized correlation phenomena in condensed-matter physics(1), has regained attention because of scanning tunnelling spectroscopy (STS) experiments carried out on single magnetic impurities(2,3). Despite the subnanometre 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 impurity(4-9). 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 calculations. These are in excellent agreement with the rich spatially and spectroscopically resolved experimental data.