Calculating Green Functions from Finite Systems

In calculating Green functions for interacting quantum systems numerically one often has to resort to finite systems which introduces a finite size level spacing. In order to describe the limit of system size going to infinity correctly, one has to introduce an artificial broadening larger than the finite size level discretization. In this work we compare various discretization schemes for impurity problems, i.e. a small system coupled to leads. Starting from a naive linear discretization we will then discuss the logarithmic discretization of the Wilson NRG, compare it to damped boundary conditions and arbitrary discretization in energy space. We then discuss the importance of choosing the right single particle basis when calculating bulk spectral functions. Finally we show the influence of damped boundary conditions on the time evolution of wave packets leading to a NRG-tsunami.Comment: 17 pages, 17 figures, accepted for publication, RFC: Please inform me about missing citation

Integrable Impurities as Boundary Conditions

A few exactly solvable interacting quantum many-body problems with impurities were previously reported to exhibit unusual features such as non-localization and absence of backscattering. In this work we consider the use of these integrable impurities as boundary conditions in the framework of linear transport problems. We first show that such impurities enhance the density of states at the Fermi surface, thus increasing the effective system size. The study of the real time-dynamics of a wave packet sent through a series of them inserted in both non-interacting and interacting leads then indicates that these impurities are transparent and do not add artefacts to the measurement of transport properties. We finally apply these new boundary conditions to study the conductance of an interacting scatterer using the embedding method.Comment: 6 figure

Color-charge separation in trapped SU(3) fermionic atoms

Cold fermionic atoms with three different hyperfine states with SU(3) symmetry confined in one-dimensional optical lattices show color-charge separation, generalizing the conventional spin charge separation for interacting SU(2) fermions in one dimension. Through time-dependent DMRG simulations, we explore the features of this phenomenon for a generalized SU(3) Hubbard Hamiltonian. In our numerical simulations of finite size systems, we observe different velocities of the charge and color degrees of freedom when a Gaussian wave packet or a charge (color) density response to a local perturbation is evolved. The differences between attractive and repulsive interactions are explored and we note that neither a small anisotropy of the interaction, breaking the SU(3) symmetry, nor the filling impedes the basic observation of these effects

A minimalistic diode

In this paper we present a minimalistic model sufficient for current asymmetries in molecules. In particular, we search for an interaction on the molecule which causes current asymmetries independent of additional assumptions or the precise form of its environment. To this end we first discuss earlier proposals and clarify the importance of additional assumptions. We then present a minimal model of a strongly polarizable molecule which shows a strongly asymmetric I/V calculated within time dependent DMRG.Comment: 6 pages, 10 figure