Toward an invariant matrix model for the Anderson Transition

Abstract: We consider invariant matrix models with log-normal (asymptotic) weight. It is known that their eigenvalue distribution is intermediate between Wigner-Dyson and Poissonian, which candidates these models for describing a system intermediate between the extended and localized phase. We show that they have a much richer energy landscape than expected, with their partition functions decomposable in a large number of equilibrium configurations, growing exponentially with the matrix rank. Within each of these saddle points, eigenvalues are uncorrelated and confined by a different potential felt by each eigenvalue. The equilibrium positions induced by the potentials differ in different saddles. Instantons connecting the different equilibrium configurations are responsible for the correlations between the eigenvalues. We argue that these instantons can be linked to the SU(2) components in which the rotational symmetry can be decomposed, paving the way to understand the conjectured critical breaking of U(N) symmetry in these invariant models.