Kondo Effect — Resonance Spectroscopy
Magnetic impurity screened by conduction electrons; Abrikosov-Suhl resonance at Fermi level
A magnetic impurity in a metal (Anderson model) is screened below the Kondo temperature T_K,
forming a spin-singlet with conduction electrons. This produces a sharp many-body resonance
at the Fermi level in the spectral function A(ω) — the Abrikosov-Suhl resonance.
Width ~ T_K; height pinned by Friedel sum rule. As T rises above T_K, the resonance broadens and
the resistance minimum (Kondo's 1964 calculation) appears. Lower panel shows resistance vs. log T.