Level statistics and localization transitions of Lévy matrices

Abstract: This work provide a thorough study of L\'evy or heavy-tailed random matrices (LM). By analysing the self-consistent equation on the probability distribution of the diagonal elements of the resolvent we establish the equation determining the localisation transition and obtain the phase diagram of LMs. Using arguments based on super-symmetric field theory and Dyson Brownian motion we show that the eigenvalue statistics is the same one of the Gaussian Orthogonal Ensemble in the whole delocalised phase and is Poisson in the localised phase. Our numerics confirms these findings, valid in the limit of infinitely large LMs, but also reveals that the characteristic scale governing finite size effects diverges much faster than a power law approaching the transition and is already very large far from it. This leads to a very wide cross-over region in which the system looks as if it were in a mixed phase. Our results, together with the ones obtained previously, provide now a complete theory of L\'evy matrices.