Fano–Kondo spin filter

The spin-dependent scanning tunneling spectrum generated by a ferromagnetic tip on a metallic host with a Kondo adatom is discussed. The combined effects of the Kondo screening, quantum interference, and tip magnetism are studied. For short tip–adatom separations, the askew lineshape characteristic of quantum interference in Kondo systems is split into two spin components. For the majority-spin component, the Fano antiresonance is strongly enhanced. With the tip atop the adatom, a window of bias voltages is found in which the tunneling current is nearly 100% spin polarized. In the vicinity of a Kondo adatom, the ferromagnetic scanning tunneling microscope constitutes a powerful spin polarizer.