15 FIG. 2: First three levels (levels 0 , 1 , and 2) in the generation process of the Wheatstone-Bridge hierarchical lattice with fractal dimension D ≈ 2 . 32. The lattice-generation process starts at the 0-th level with a single bond and at each step a bond is replaced by its respective basic cell. In each level, the empty circles ( µ and ν ) represent the external sites of the lattice, whereas the black circles are internal sites to be decimated in successive RG operations.