"Entanglement entropy of low-lying excitation in localized interacting system: Signature of Fock space delocalization"

The properties of the entanglement entropy (EE) of low-lying excitations in one-dimensional disordered interacting systems are described. The ground state EE shows a clear signature of localization, while low-lying excitations show a significantly longer localization length. The dependence of the localization as function of interaction strength and sample length is studied using the density matrix renormalization group (DMRG). This behavior corresponds to the presence of the predicted many particle critical energy in the vicinity of the ground state energy. Implications of these results to experiments are discussed.