Theory for Anomalous NMR Response in Pb_(1-x)Tl_(x)Te on Charge Kondo Effect

A theory for anomalous enhancement of NMR relaxation rate $1/T_{1}T$ of $^{125}$Te toward zero temperature observed in Pb$_{1-x}$Tl$_{x}$Te ($x$=0.01) is presented on the idea of the charge Kondo effect of valence skipping element Tl. It is found that such enhancement in $1/T_{1}T$ is caused through enhancement of the pair-hopping and inter-orbital interactions between 6s electrons localized on Tl site and conduction electrons doped in the hole band the semiconductor PbTe, which is the heart of the charge Kondo effect. It is also found that the Knight shift is not influenced in the temperature region where the relaxation rate is enhanced which is consistent with the experimental observation showing that the Korringa relation is apparently broken.