Nonequilibrium Quasiparticle Distribution Induced by Kondo Defects

It is shown that in resistive nanowires out of equilibrium containing either single- or two-channel Kondo impurities the distribution function $f(E,U)$ obeys scaling behavior in terms of the quasiparticle energy $E$ and the bias voltage $U$. The numerically calculated $f(E,U)$ curves explain quantitatively recent experiments on Cu and Au nanowires. The systematics of the impurity concentration $c_{\mathrm{imp}}$ extracted from the comparison between theory and results on various Cu and Au samples strongly suggests that in these systems the scaling arises from magnetic Kondo impurities.