Dyson’s Spike for Random Schroedinger Operators and Novikov–Shubin Invariants of Groups

We study one dimensional Schroedinger operators with random edge weights and their expected spectral measures μ_H near zero. We prove that the measure exhibits a spike of the form μ_H(-ε,ε) ∼C/| logε|^2 (first observed by Dyson), without assuming independence or any regularity of edge weights. We also identify the limiting local eigenvalue distribution, which is different from Poisson and the usual random matrix statistics. We then use the result to compute Novikov–Shubin invariants for various groups, including lamplighter groups and lattices in the Lie group Sol.