Electronic states on a fractal: Exact Green's-function renormalization approach

Abstract

A nontrivial tight-binding model for electron dynamics on the fractal Koch curve is investigated within the framework of the Green s-function formalism. The key result is the construction of a multiple exact renormalization group that allows one to derive all the rather unusual properties of the model. This group is generated by four nonequivalent decimation operations, which define distinct transforrnation rules for the 48 relevant parameters to be renormalized. The calculation of the density of states confirms the crucial results that were obtained recently using transfer-matrix methods: local self-amenity, dense gap structure, and singular electronic levels with infinite degeneracy. This demonstrates that the Green s-function approach is not inferior to other techniques even in topologically one-dimensional situations.