Quasiparticles in Anderson Insulators : a Scenario of Delocalization induced by Interactions

Oleg I. Utesov

Felix von Oppen, Tilo Wettig B

It has recently been established that a short-range interaction can strongly delocalize a pair of particles moving in a disordered potential. We investigate whether an analogous effect exists also for pairs of quasiparticles in the Anderson insulator by employing an approximate numerical evaluation of the two-particle Green function of the many-body system. At the Fermi energy, the quasiparticle pair is localized on the scale of the single-particle localization length. The delocalization effect is recovered when the excitation energy of the pair is comparable to the bandwidth.

Philippe Jacquod

The localization properties of quasiparticle pairs above a frozen Fermi sea in the two- and three-dimensional Anderson model with Hubbard interaction are investigated. The dependence of the width Γ of the local spectral density on the pair excitation energy ε2, the disorder W, the interaction strength U and the linear system size L is determined. The obtained results allow to emphasize an interaction-induced pair delocalization effect even when the quasiparticles remain individually localized. The corresponding mobility edge is further estimated and the disorder versus interaction phase diagram is determined. Further investigations focusing on the spectral properties of the system and the transition from Poisson to Wigner-Dyson statistics corroborate these conclusions. The relevance of this effect with respect to the one-quasiparticle lifetime is finally discussed.

Benjamin Deissler, Chiara D’Errico, M. Fattori +5 more

Andrzej M. Oleś, Barbara Oleś

Filippo Stellin, Giuliano Orso

Abstract We review our recent results on Anderson localization in systems of two interacting particles coupled by contact interactions. Based on an exact mapping to an effective single-particle problem, we numerically investigate the occurrence of metal-insulator phase transitions for the pair in two-(2D) and three-dimensional (3D) disordered lattices. In two dimensions, we find that interactions cause an exponential enhancement of the pair localization length with respect to its single-particle counterpart, but do not induce a delocalization transition. In particular we show that previous claims of 2D interaction-induced Anderson transitions are the results of strong finite-size effects. In three dimensions we find that the pair undergoes a metal-insulator transition belonging to the same (orthogonal) universality class of the noninteracting model. We then explore the phase diagram in the space of energy E, disorder W and interaction strength U, which reveals a rich and counterintuitive structure, endowed with multiple metallic and insulating phases. We point out that this phenomenon originates from the molecular and scattering-like nature of the pair states available at given energy and disorder strength.