5,140 research outputs found
Nonequilibrium functional renormalization group for interacting quantum systems
We propose a nonequilibrium version of functional renormalization within the
Keldysh formalism by introducing a complex valued flow parameter in the Fermi
or Bose functions of each reservoir. Our cutoff scheme provides a unified
approach to equilibrium and nonequilibrium situations. We apply it to
nonequilibrium transport through an interacting quantum wire coupled to two
reservoirs and show that the nonequilibrium occupation induces new power law
exponents for the conductance.Comment: 5 pages, 2 figures; published versio
Functional renormalization group study of the Anderson--Holstein model
We present a comprehensive study of the spectral and transport properties in
the Anderson--Holstein model both in and out of equilibrium using the
functional renormalization group (FRG). We show how the previously established
machinery of Matsubara and Keldysh FRG can be extended to include the local
phonon mode. Based on the analysis of spectral properties in equilibrium we
identify different regimes depending on the strength of the electron--phonon
interaction and the frequency of the phonon mode. We supplement these
considerations with analytical results from the Kondo model. We also calculate
the non-linear differential conductance through the Anderson--Holstein quantum
dot and find clear signatures of the presence of the phonon mode.Comment: 19 pages, 8 figure
Leading-logarithmic approximation by one-loop renormalization group within Matsubara formalism
We demonstrate how to devise a Matsubara-formalism based one-loop
approximation to the flow of the functional renormalization group (FRG) that
reproduces identically the leading-logarithmic parquet approximation. This
construction of a controlled fermionic FRG approximation in a regime not
accessible by perturbation theory generalizes a previous study from the
real-time zero-temperature formalism to the Matsubara formalism and thus to the
de facto standard framework used for condensed-matter FRG studies. Our
investigation is based on a simple model for the absorption of x-rays in
metals. It is a core part of our construction to exploit that in a suitable
leading-logarithmic approximation the values of the particle-hole
susceptibility on the real and on the imaginary frequency axis are identical.Comment: 20 pages, 7 figure
Comparative study of theoretical methods for nonequilibrium quantum transport
We present a detailed comparison of three different methods designed to
tackle nonequilibrium quantum transport, namely the functional renormalization
group (fRG), the time-dependent density matrix renormalization group (tDMRG),
and the iterative summation of real-time path integrals (ISPI). For the
nonequilibrium single-impurity Anderson model (including a Zeeman term at the
impurity site), we demonstrate that the three methods are in quantitative
agreement over a wide range of parameters at the particle-hole symmetric point
as well as in the mixed-valence regime. We further compare these techniques
with two quantum Monte Carlo approaches and the time-dependent numerical
renormalization group method.Comment: 19 pages, 7 figures; published versio
Temperature induced phase averaging in one-dimensional mesoscopic systems
We analyse phase averaging in one-dimensional interacting mesoscopic systems
with several barriers and show that for incommensurate positions an independent
average over several phases can be induced by finite temperature. For three
strong barriers with conductances G_i and mutual distances larger than the
thermal length, we obtain G ~ sqrt{G_1 G_2 G_3} for the total conductance G.
For an interacting wire, this implies power laws in G(T) with novel exponents,
which we propose as an experimental fingerprint to distinguish temperature
induced phase averaging from dephasing.Comment: 6 pages, 5 figures; added one figure; slightly extende
Exact results for nonlinear ac-transport through a resonant level model
We obtain exact results for the transport through a resonant level model
(noninteracting Anderson impurity model) for rectangular voltage bias as a
function of time. We study both the transient behavior after switching on the
tunneling at time t = 0 and the ensuing steady state behavior. Explicit
expressions are obtained for the ac-current in the linear response regime and
beyond for large voltage bias. Among other effects, we observe current ringing
and PAT (photon assisted tunneling) oscillations.Comment: 7 page
A renormalization group approach to time dependent transport through correlated quantum dots
We introduce a real time version of the functional renormalization group
which allows to study correlation effects on nonequilibrium transport through
quantum dots. Our method is equally capable to address (i) the relaxation out
of a nonequilibrium initial state into a (potentially) steady state driven by a
bias voltage and (ii) the dynamics governed by an explicitly time-dependent
Hamiltonian. All time regimes from transient to asymptotic can be tackled; the
only approximation is the consistent truncation of the flow equations at a
given order. As an application we investigate the relaxation dynamics of the
interacting resonant level model which describes a fermionic quantum dot
dominated by charge fluctuations. Moreover, we study decoherence and relaxation
phenomena within the ohmic spin-boson model by mapping the latter to the
interacting resonant level model
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