Real space renormalization and the anderson model in one dimension

James H. Luscombe, Gene F. Mazenko

James Franck Institute

Yoshitake Yamazaki, G�nther Meissner, Henk J. Hilhorst

Theodore W. Burkhardt, J. M. J. van Leeuwen

Donovan James McMurrich Allum

S. Johri and R. Bhatt developed a real-space renormalization group approach aimed at extracting the localized single-particle eigenstates of the Anderson model from a large system by identifying clusters of resonant site potentials. E. Campbell generalized this real-space renormalization group approach using standard perturbation theory. Both approaches were intended to approximate the single-particle density of states of the Anderson model. In this thesis, we aimed to test the potential of applying a similar real-space renormalization group approach to calculate the density of states of the interacting Anderson-Hubbard model. Our interest in the density of states of this model is due to a V-shaped zero-bias anomaly in two-dimensional systems. A real-space renormalization group approach is best applied to a one-dimensional system. We found that the zero-bias anomaly is not V-shaped in one-dimension. To test the potential of a real-space renormalization group approach, we used the cluster approach which is the same as the non-interacting renormalization group approach but without the perturbation theory and found that for strong disorder this technique could accurately calculate the density of states over a wide range of energies but deviated from exact results at the band edge, at $omega=pm U$ and near $omega=0$. The first two inaccuracies will be reduced with a proper real-space renormalization group approach. We suspect that the last inaccuracy is associated with long range physics and may be difficult to recover. We also developed a technique that adjusts the identification of clusters in the cluster approach to improve the computation time of the density of states with minimal loss of accuracy in a tunable range around the Fermi level. We found that this technique significantly reduced the computation time and was able to preserve the density of states near the Fermi level, except at the smallest energies near $omega=0$. Author Keywords: Anderson-Hubbard model, renormalization group, Strong electron correlations, Zero-bias anomaly

R. M. Noack, Steven R. White

We discuss the application of a quantum real-space renormalization-group approach to the Anderson-localization problem. States obtained by applying combinations of fixed and free boundary conditions to the system are used as a truncated basis at each iteration. We discuss the problem of intruder states, which occurs when the renormalization-group procedure is used to find states at the center of the band; we also discuss some possible solutions. We present numerical results for the conductance, the localization length, and the scaling function for the Anderson-localization problem in one dimension.