Study of the Localization Transition on a Cayley-tree via Spectral Statistics

The spectral statistics of a Cayley-tree is numerically studied. The statistics are non-universal due to the high ratio of boundary sites. Once the boundary sites are connected to each other in a way that preserves the local structure of the tree the universal statistics of the spectra is recovered. A clear localization transition is observed as function of on-site disorder strength, with a critical disorder $W_c=11.44^{+0.08}_{-0.04}$ and critical index $\nu=0.51^{+0.05}_{-0.04}$. The value of $\nu$ fits nicely to its mean field value, while the value of $W_c$ is puzzling.