文摘
We introduce a new class of noncommutative spectral triples on Kellendonk’s C∗C∗-algebra associated with a nonperiodic substitution tiling. These spectral triples are constructed from fractal trees on tilings, which define a geodesic distance between any two tiles in the tiling. Since fractals typically have infinite Euclidean length, the geodesic distance is defined using Perron–Frobenius theory, and is self-similar with scaling factor given by the Perron–Frobenius eigenvalue. We show that each spectral triple is θθ-summable, and respects the hierarchy of the substitution system. To elucidate our results, we construct a fractal tree on the Penrose tiling, and explicitly show how it gives rise to a collection of spectral triples.