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

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

Invariants of the single impurity Anderson model and implications for conductance functionals

An exact relation between the conductance maximum $G_0$ at zero temperature and a ratio of lead densities is derived within the framework of the single impurity Anderson model: $G_0={\mathfrak R}[n] \frac{2e^2}{h}$, where ${\mathfrak R}[n]=4\Delta N_{{\cal L},x} \Delta N_{{\cal R},x}/(\Delta N_{{\cal L},x}+\Delta N_{{\cal R},x})^2$ and $\Delta N_{{\cal L},x}$, $\Delta N_{{\cal R},x}$ denote the excess density in the left/right lead at distance $x$ due to the presence of the impurity at the origin, $x=0$. The relation constitutes a parameter-free expression of the conductance of the model in terms of the ground state density that generalizes an earlier result to the generic case of asymmetric lead couplings. It turns out that the specific density ratio, ${\mathfrak R}[n]$, is independent of the distance to the impurity $x$, the (magnetic) band-structure and filling fraction of the contacting wires, the strength of the onsite interaction, the gate voltage and the temperature. Disorder induced backscattering in the contacting wires has an impact on ${\mathfrak R}$ that we discuss. Our result suggests that it should be possible, in principle, to determine experimentally the peak conductance of the Anderson impurity by performing a combination of measurements of ground-state densities.Comment: 5 pages, 3 figures, accepted by EP