Two or More Impurities; Disordered Systems
In this chapter we examine first a system consisting of two “impurities” embedded in a periodic tight binding hamiltonian (TBH). The total t-matrix associated with the two impurities is not simply the sum of t-matrices of each impurity but includes infinitely many terms which correspond physically to multiple scattering events. A diagrammatic representation of this fact is shown in Fig.7.1, where the propagation from site i to site j [described by G(i,j)] is decomposed to unperturbed propagations [described by G (n,n’)] and scattering events (described by the t-matrices T l , T m ) from the impurity sites l and m.
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