136 research outputs found
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
Junctions of one-dimensional quantum wires - correlation effects in transport
We investigate transport of spinless fermions through a single site dot
junction of M one-dimensional quantum wires. The semi-infinite wires are
described by a tight-binding model. Each wire consists of two parts: the
non-interacting leads and a region of finite extent in which the fermions
interact via a nearest-neighbor interaction. The functional renormalization
group method is used to determine the flow of the linear conductance as a
function of a low-energy cutoff for a wide range of parameters. Several fixed
points are identified and their stability is analyzed. We determine the scaling
exponents governing the low-energy physics close to the fixed points. Some of
our results can already be derived using the non-self-consistent Hartree-Fock
approximation.Comment: version accepted for publication in Phys. Rev. B, 14 pages, 7 figures
include
Features of spin-charge separation in the equilibrium conductance through finite rings
We calculate the conductance through rings with few sites described by
the model, threaded by a magnetic flux and weakly coupled to
conducting leads at two arbitrary sites. The model can describe a circular
array of quantum dots with large charging energy in comparison with the
nearest-neighbor hopping . We determine analytically the particular values
of for which a depression of the transmittance is expected as a
consequence of spin-charge separation. We show numerically that the equilibrium
conductance at zero temperature is depressed at those particular values of
for most systems, in particular at half filling, which might be easier
to realize experimentally.Comment: 8 pages, 7 figure
Spin-charge separation in strongly interacting finite ladder rings
We study the conductance through Aharonov-Bohm finite ladder rings with
strongly interacting electrons, modelled by the prototypical t-J model. For a
wide range of parameters we observe characteristic dips in the conductance as a
function of magnetic flux, predicted so far only in chains which are a
signature of spin and charge separation. These results open the possibility of
observing this peculiar many-body phenomenon in anisotropic ladder systems and
in real nanoscopic devices.Comment: 4 pages, 6 figure
Effects of Disorder and Momentum Relaxation on the Intertube Transport of Incommensurate Carbon Nanotube Ropes and Multiwall Nanotubes
We study theoretically the electrical transport between aligned carbon
nanotubes in nanotube ropes, and between shells in multiwall carbon nanotubes.
We focus on transport between two metallic nanotubes (or shells) of different
chiralities with mismatched Fermi momenta and incommensurate periodicities. We
perform numerical calculations of the transport properties of such systems
within a tight-binding formalism. For clean (disorder-free) nanotubes the
intertube transport is strongly suppressed as a result of momentum
conservation. For clean nanotubes, the intertube transport is typically
dominated by the loss of momentum conservation at the contacts. We discuss in
detail the effects of disorder, which also breaks momentum conservation, and
calculate the effects of localised scatterers of various types. We show that
physically relevant disorder potentials lead to very dramatic enhancements of
the intertube conductance. We show that recent experimental measurements of the
intershell transport in multiwall nanotubes are consistent with our theoretical
results for a model of short-ranged correlated disorder.Comment: References adde
Canonically conjugate pairs and phase operators
For quantum mechanics on a lattice the position (``particle number'')
operator and the quasi-momentum (``phase'') operator obey canonical commutation
relations (CCR) only on a dense set of the Hilbert space. We compare exact
numerical results for a particle in simple potentials on the lattice with the
expectations, when the CCR are assumed to be strictly obeyed. Only for
sufficiently smooth eigenfunctions this leads to reasonable results. In the
long time limit the use of the CCR can lead to a qualitativel wrong dynamics
even if the initial state is in the dense set.Comment: 4 pages, 5 figures. Phys. Rev. A, in pres
Nonuniversal spectral properties of the Luttinger model
The one electron spectral functions for the Luttinger model are discussed for
large but finite systems. The methods presented allow a simple interpretation
of the results. For finite range interactions interesting nonunivesal spectral
features emerge for momenta which differ from the Fermi points by the order of
the inverse interaction range or more. For a simplified model with interactions
only within the branches of right and left moving electrons analytical
expressions for the spectral function are presented which allows to perform the
thermodynamic limit. As in the general spinless model and the model including
spin for which we present mainly numerical results the spectral functions do
not approach the noninteracting limit for large momenta. The implication of our
results for recent high resolution photoemission measurements on quasi
one-dimensional conductors are discussed.Comment: 19 pages, Revtex 2.0, 5 ps-figures, to be mailed on reques
Spin-charge separation in transport through Luttinger liquid rings
We investigate how the different velocities characterizing the low-energy
spectral properties and the low-temperature thermodynamics of one-dimensional
correlated electron systems (Luttinger liquids) affect the transport properties
of ring-like conductors. The Luttinger liquid ring is coupled to two
noninteracting leads and pierced by a magnetic flux. We study the flux
dependence of the linear conductance. It shows a dip structure which is
governed by the interaction dependent velocities. Our work extends an earlier
study which was restricted to rather specific choices of the interaction
parameters. We show that for generic repulsive two-particle interactions the
number of dips can be estimated from the ratio of the charge current velocity
and the spin velocity. In addition, we clarify the range of validity of the
central approximation underlying the earlier study.Comment: 10 pages including figure
Newton's law for Bloch electrons, Klein factors and deviations from canonical commutation relations
The acceleration theorem for Bloch electrons in a homogenous external field
is usually presented using quasiclassical arguments. In quantum mechanical
versions the Heisenberg equations of motion for an operator
are presented mostly without properly defining this operator. This leads to the
surprising fact that the generally accepted version of the theorem is incorrect
for the most natural definition of . This operator is shown not
to obey canonical commutation relations with the position operator. A similar
result is shown for the phase operators defined via the Klein factors which
take care of the change of particle number in the bosonization of the field
operator in the description of interacting fermions in one dimension. The phase
operators are also shown not to obey canonical commutation relations with the
corresponding particle number operators. Implications of this fact are
discussed for Tomonaga-Luttinger type models.Comment: 9 pages,1 figur
Confined coherence and analytic properties of Green's functions
A simple model of noninteracting electrons with a separable one-body
potential is used to discuss the possible pole structure of single particle
Green's functions for fermions on unphysical sheets in the complex frequency
plane as a function of the system parameters. The poles in the exact Green's
function can cross the imaginary axis, in contrast to recent claims that such a
behaviour is unphysical. As the Green's function of the model has the same
functional form as an approximate Green's function of coupled Luttinger liquids
no definite conclusions concerning the concept of "confined coherence" can be
drawn from the locations of the poles of this Green's function.Comment: 3 pages, 3 figure
- …