New spectroscopy solves an old puzzle: the Kondo scale in heavy fermions.
Resonant inelastic x-ray scattering (RIXS) yields clear evidence of spectroscopic Kondo scales in heavy fermions. In YbInCu4 and YbAgCu4 RIXS probes the Yb2+ component of the hybrid ground state and the temperature dependence of the Yb 4f occupation. We report a sudden valence change at a phase transition in YbInCu4, but a continuous temperature dependence in YbAgCu4, consistent with the predictions of the Anderson impurity model, for a Kondo temperature T(K) = 70 K. These results solve a long-standing controversy and establish RIXS as a quantitative probe of the electronic structure of strongly correlated electron systems.
Dallera
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C
INFM-Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133 Milano, Italy.
Grioni
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M
Shukla
A
A
Vankó
G
G
Sarrao
J L
JL
Rueff
J P
JP
Cox
D L
DL