Localized phase for the Erd\H{o}s-R\'enyi graph

TL;DR

This paper investigates the eigenvector localization in Erdős-Rényi graphs, identifying a localized phase near the delocalized phase boundary and providing explicit asymptotics for localization length.

Contribution

It introduces a rigorous analysis of the localized phase in Erdős-Rényi graphs, including the existence of a mobility edge and detailed asymptotics for localization length.

Findings

Existence of a localized phase near the delocalized boundary.

Explicit asymptotics for localization length.

Identification of a mobility edge for large degrees.

Abstract

We analyse the eigenvectors of the adjacency matrix of the Erd\H{o}s-R\'enyi graph $\mathbb G(N,d/N)$ for $\sqrt{\log N} \ll d \lesssim \log N$. We show the existence of a localized phase, where each eigenvector is exponentially localized around a single vertex of the graph. This complements the completely delocalized phase previously established in [arXiv:2005.14180]. For large enough $d$, we establish a mobility edge by showing that the localized phase extends up to the boundary of the delocalized phase. We derive explicit asymptotics for the localization length up to the mobility edge and characterize its divergence near the phase boundary. The proof is based on a rigorous verification of Mott's criterion for localization, comparing the tunnelling amplitude between localization centres with the eigenvalue spacing. The first main ingredient is a new family of global approximate eigenvectors, for which sharp enough estimates on the tunnelling amplitude can be established. The second main ingredient is a lower bound on the spacing of approximate eigenvalues. It follows from an anticoncentration result for these discrete random variables, obtained by a recursive application of a self-improving anticoncentration estimate due to Kesten.