243 research outputs found
Kondo physics in transport through a quantum dot with Luttinger liquid leads
We study the gate voltage dependence of the linear conductance through a
quantum dot coupled to one-dimensional leads. For interacting dot electrons but
noninteracting leads Kondo physics implies broad plateau-like resonances. In
the opposite case Luttinger liquid behavior leads to sharp resonances. In the
presence of Kondo as well as Luttinger liquid physics and for experimentally
relevant parameters, we find a line shape that resembles the one of the Kondo
case.Comment: 4+ pages, 4 figures include
Nonequilibrium thermoelectric transport through vibrating molecular quantum dots
We employ the functional renormalization group to study the effects of
phonon-assisted tunneling on the nonequilibrium steady-state transport through
a single level molecular quantum dot coupled to electronic leads. Within the
framework of the spinless Anderson-Holstein model, we focus on small to
intermediate electron-phonon couplings, and we explore the evolution from the
adiabatic to the antiadiabatic limit and also from the low-temperature
non-perturbative regime to the high temperature perturbative one. We identify
the phononic signatures in the bias-voltage dependence of the electrical
current and the differential conductance. Considering a temperature gradient
between the electronic leads, we further investigate the interplay between the
transport of charge and heat. Within the linear response regime, we compare the
temperature dependence of various thermoelectric coefficients to our earlier
results obtained within the numerical renormalization group [Phys.~Rev.~B {\bf
96}, 195156 (2017)]. Beyond the linear response regime, in the context of
thermoelectric generators, we discuss the influence of molecular vibrations on
the output power and the efficiency. We find that the molecular energy
dissipation, which is inevitable in the presence of phonons, is significantly
suppressed in the antiadiabatic limit resulting in the enhancement of the
thermoelectric efficiency.Comment: 11 pages, 7 figures, Published versio
Influence of phonon-assisted tunneling on the linear thermoelectric transport through molecular quantum dots
We investigate the effect of vibrational degrees of freedom on the linear
thermoelectric transport through a single-level quantum dot described by the
spinless Anderson-Holstein impurity model. To study the effects of strong
electron-phonon coupling, we use the nonperturbative numerical renormalization
group approach. We also compare our results, at weak to intermediate coupling,
with those obtained by employing the functional renormalization group method,
finding good agreement in this parameter regime. When applying a gate voltage
at finite temperatures, the inelastic scattering processes, induced by
phonon-assisted tunneling, result in an interesting interplay between
electrical and thermal transport. We explore different parameter regimes and
identify situations for which the thermoelectric power as well as the
dimensionless figure of merit are significantly enhanced via a Mahan-Sofo type
of mechanism. We show, in particular, that this occurs at strong
electron-phonon coupling and in the antiadiabatic regime.Comment: 14 pages, 8 figures, Published versio
Exponential and power-law renormalization in phonon-assisted tunneling
We investigate the spinless Anderson-Holstein model routinely employed to
describe the basic physics of phonon-assisted tunneling in molecular devices.
Our focus is on small to intermediate electron-phonon coupling; we complement a
recent strong coupling study [Phys.~Rev.~B {87}, 075319 (2013)]. The entire
crossover from the antiadiabatic regime to the adiabatic one is considered. Our
analysis using the essentially analytical functional renormalization group
approach backed-up by numerical renormalization group calculations goes beyond
lowest order perturbation theory in the electron-phonon coupling. In
particular, we provide an analytic expression for the effective tunneling
coupling at particle-hole symmetry valid for all ratios of the bare tunnel
coupling and the phonon frequency. It contains the exponential polaronic as
well as the power-law renormalization; the latter can be traced back to x-ray
edge-like physics. In the antiadiabatic and the adiabatic limit this expression
agrees with the known ones obtained by mapping to an effective interacting
resonant level model and lowest order perturbation theory, respectively. Away
from particle-hole symmetry, we discuss and compare results from several
approaches for the zero temperature electrical conductance of the model.Comment: 11 pages, 6 figures, Published versio
Pseudogap at hot spots in the two-dimensional Hubbard model at weak coupling
We analyze the interaction-induced renormalization of single-particle
excitations in the two-dimensional Hubbard model at weak coupling using the
Wick-ordered version of the functional renormalization group. The self energy
is computed for real frequencies by integrating a flow equation with
renormalized two-particle interactions. In the vicinity of hot spots, that is
points where the Fermi surface intersects the umklapp surface, self energy
effects beyond the usual quasi-particle renormalizations and damping occur near
instabilities of the normal, metallic phase. Strongly enhanced renormalized
interactions between particles at different hot spots generate a pronounced
low-energy peak in the imaginary part of the self energy, leading to a
pseudogap-like double-peak structure in the spectral function for
single-particle excitations.Comment: 14 pages, 7 figure
Luttinger liquids with boundaries: Power-laws and energy scales
We present a study of the one-particle spectral properties for a variety of
models of Luttinger liquids with open boundaries. We first consider the
Tomonaga-Luttinger model using bosonization. For weak interactions the boundary
exponent of the power-law suppression of the spectral weight close to the
chemical potential is dominated by a term linear in the interaction. This
motivates us to study the spectral properties also within the Hartree-Fock
approximation. It already gives power-law behavior and qualitative agreement
with the exact spectral function. For the lattice model of spinless fermions
and the Hubbard model we present numerically exact results obtained using the
density-matrix renormalization-group algorithm. We show that many aspects of
the behavior of the spectral function close to the boundary can again be
understood within the Hartree-Fock approximation. For the repulsive Hubbard
model with interaction U the spectral weight is enhanced in a large energy
range around the chemical potential. At smaller energies a power-law
suppression, as predicted by bosonization, sets in. We present an analytical
discussion of the crossover and show that for small U it occurs at energies
exponentially (in -1/U) close to the chemical potential, i.e. that bosonization
only holds on exponentially small energy scales. We show that such a crossover
can also be found in other models.Comment: 16 pages, 9 figures included, submitted for publicatio
Renormalization-group analysis of the one-dimensional extended Hubbard model with a single impurity
We analyze the one-dimensional extended Hubbard model with a single static
impurity by using a computational technique based on the functional
renormalization group. This extends previous work for spinless fermions to
spin-1/2 fermions. The underlying approximations are devised for weak
interactions and arbitrary impurity strengths, and have been checked by
comparing with density-matrix renormalization-group data. We present results
for the density of states, the density profile and the linear conductance.
Two-particle backscattering leads to striking effects, which are not captured
if the bulk system is approximated by its low-energy fixed point, the Luttinger
model. In particular, the expected decrease of spectral weight near the
impurity and of the conductance at low energy scales is often preceded by a
pronounced increase, and the asymptotic power laws are modified by logarithmic
corrections.Comment: 36 pages, 13 figures, revised version as publishe
Probing electron-electron interaction in quantum Hall systems with scanning tunneling spectroscopy
Using low-temperature scanning tunneling spectroscopy applied to the
Cs-induced two-dimensional electron system (2DES) on p-type InSb(110), we probe
electron-electron interaction effects in the quantum Hall regime. The 2DES is
decoupled from p-doped bulk states and exhibits spreading resistance within the
insulating quantum Hall phases. In quantitative agreement with calculations we
find an exchange enhancement of the spin splitting. Moreover, we observe that
both the spatially averaged as well as the local density of states feature a
characteristic Coulomb gap at the Fermi level. These results show that
electron-electron interaction effects can be probed down to a resolution below
all relevant length scales.Comment: supplementary movie in ancillary file
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