Hamiltonian of interaction between fixed ion and conducting electron(adsbygoogle = window.adsbygoogle || []).push({});

##\hat{H}=-J\sum_{i=1}^2\{\hat{s}_i^z\hat{S}_i^z+\frac{1}{2}(\hat{s}_i^+\hat{S}_i^{-}+\hat{s}_i^-\hat{S}_i^{+})\}##

Why both electron and ion are defined with subscript ##i##?

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# RKKY interraction

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