Well-defined quasiparticles in interacting metallic grains
  We analyze spectral functions of mesoscopic systems with large dimensionless conductance, which can be described by a universal Hamiltonian. We show that an important class of spectral functions are dominated by one single state only, which implies the existence of well-defined (i.e. infinite-lifetime) quasiparticles. Furthermore, the dominance of a single state enables us to calculate zero-temperature spectral functions with high accuracy using the density-matrix renormalization group. We illustrate the use of this method by calculating the tunneling density of states of metallic grains and the magnetic response of mesoscopic rings. 
Dominique Gobert, Moshe Schechter, Ulrich Schollwock, Jan von Delft