193 research outputs found
Influence of the contacts on the conductance of interacting quantum wires
We investigate how the conductance G through a clean interacting quantum wire
is affected by the presence of contacts and noninteracting leads. The contacts
are defined by a vanishing two-particle interaction to the left and a finite
repulsive interaction to the right or vice versa. No additional single-particle
scattering terms (impurities) are added. We first use bosonization and the
local Luttinger liquid picture and show that within this approach G is
determined by the properties of the leads regardless of the details of the
spatial variation of the Luttinger liquid parameters. This generalizes earlier
results obtained for step-like variations. In particular, no single-particle
backscattering is generated at the contacts. We then study a microscopic model
applying the functional renormalization group and show that the spatial
variation of the interaction produces single-particle backscattering, which in
turn leads to a reduced conductance. We investigate how the smoothness of the
contacts affects G and show that for decreasing energy scale its deviation from
the unitary limit follows a power law with the same exponent as obtained for a
system with a weak single-particle impurity placed in the contact region of the
interacting wire and the leads.Comment: 10 page, 4 figures included, minor changes in the summary, version
accepted for publication in PR
Charging of a quantum dot coupled to Luttinger liquid leads
Luttinger liquid behavior of one-dimensional correlated electron systems is
characterized by power-law scaling of a variety of physical observables with
exponents determined by a single interaction dependent parameter K. We suggest
a setup to study Luttinger liquid behavior in quantum wires which allows to
determine K from two independent measurements: resonant transport through a
quantum dot embedded in the wire and the charge on the dot. Consistency of the
two measured values of K for a single probe would provide strong experimental
evidence for the Luttinger liquid paradigm.Comment: 4 pages, 4 figures included, version accepted for publication in PR
A junction of three quantum wires: restoring time-reversal symmetry by interaction
We investigate transport of correlated fermions through a junction of three
one-dimensional quantum wires pierced by a magnetic flux. We determine the flow
of the conductance as a function of a low-energy cutoff in the entire parameter
space. For attractive interactions and generic flux the fixed point with
maximal asymmetry of the conductance is the stable one, as conjectured
recently. For repulsive interactions and arbitrary flux we find a line of
stable fixed points with vanishing conductance as well as stable fixed points
with symmetric conductance (4/9)(e^2/h).Comment: 5 pages, 3 figures, version accepted for publication in Phys. Rev.
Let
Comment on "Canonical and Mircocanonical Calculations for Fermi Systems"
In the context of nuclear physics Pratt recently investigated noninteracting
Fermi systems described by the microcanonical and canonical ensemble. As will
be shown his discussion of the model of equally spaced levels contains a flaw
and a statement which is at least confusing.Comment: Comment on S. Pratt, Phys. Rev. Lett. 84, 4255 (2000) and
nucl-th/990505
Finite-temperature linear conductance from the Matsubara Green function without analytic continuation to the real axis
We illustrate how to calculate the finite-temperature linear-response
conductance of quantum impurity models from the Matsubara Green function. A
continued fraction expansion of the Fermi distribution is employed which was
recently introduced by Ozaki [Phys. Rev. B 75, 035123 (2007)] and converges
much faster than the usual Matsubara representation. We give a simplified
derivation of Ozaki's idea using concepts from many-body condensed matter
theory and present results for the rate of convergence. In case that the Green
function of some model of interest is only known numerically, interpolating
between Matsubara frequencies is much more stable than carrying out an analytic
continuation to the real axis. We demonstrate this explicitly by considering an
infinite tight-binding chain with a single site impurity as an exactly-solvable
test system, showing that it is advantageous to calculate transport properties
directly on the imaginary axis. The formalism is applied to the single impurity
Anderson model, and the linear conductance at finite temperatures is calculated
reliably at small to intermediate Coulomb interactions by virtue of the
Matsubara functional renormalization group. Thus, this quantum many-body method
combined with the continued fraction expansion of the Fermi function
constitutes a promising tool to address more complex quantum dot geometries at
finite temperatures.Comment: version accepted by Phys. Rev.
Indirect forces between impurities in one-dimensional quantum liquids
We investigate the indirect interaction between two isolated impurities in a
Luttinger liquid described by a microscopic lattice model. To treat the
electron-electron interaction U the functional renormalization group method is
used. For comparison we also study the U=0 case. We find that for a wide range
of impurity parameters the impurity interaction V_{12} as a function of their
separation r oscillates with decaying amplitude between being attractive and
repulsive. For half-filling of the band and in a crossover regime between weak
and strong impurities the interaction becomes purely attractive. For U=0 and
independent of the impurity strength the amplitude of the interaction energy
falls off as 1/r. For U>0 the decay for small separations and weak to
intermediate impurities is governed by a U dependent exponent larger than -1,
which crosses over to -1 for large r. The crossover scale depends on the
impurity strength and U. We present simple pictures which explain our results
in the limits of weak and strong impurities. We finally also consider
attractive interactions U<0.Comment: 8 pages, 9 figures include
Comment on ``Bethe Ansatz Results for the 4f-Electron Spectra of a Degenerate Anderson Model ''
In a recent letter, Zvyagin calculates the density of states for 4f electrons
coupled to a conduction band in the framework of the Bethe ansatz (BA) solution
for the degenerate Anderson model. It is claimed that the results qualitatively
disagree with the results obtained for the same model but using a variational
approach. Even the high energy feature in the f-spectral function near the
4f-level energy ef, i.e. the ``normal'' ionization peak (NIP), is argued to be
qualitatively different in the two approaches. In the following we point out
that this is not the case.Comment: 1 page, RevTeX, no figur
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