126 research outputs found
Interference effects in interacting quantum dots
In this paper we study the interplay between interference effects in quantum
dots (manifested through the appearance of Fano resonances in the conductance),
and interactions taken into account in the self-consistent Hartree-Fock
approximation. In the non-interacting case we find that interference may lead
to the observation of more than one conductance peak per dot level as a
function of an applied gate voltage. This may explain recent experimental
findings, which were thought to be caused by interaction effects. For the
interacting case we find a wide variety of different interesting phenomena.
These include both monotonous and non-monotonous filling of the dot levels as a
function of an applied gate voltage, which may occur continuously or even
discontinuously. In many cases a combination of the different effects can occur
in the same sample. The behavior of the population influences, in turn, the
conductance lineshape, causing broadening and asymmetry of narrow peaks, and
determining whether there will be a zero transmission point. We elucidate the
essential role of the interference between the dot levels in determining these
outcomes. The effects of finite temperatures on the results are also examined.Comment: 11 pages, 9 fugures, REVTeX
Transport Properties of Multiple Quantum Dots Arranged in Parallel: Results from the Bethe Ansatz
In this paper we analyze transport through a double dot system connected to
two external leads. Imagining each dot possessing a single active level, we
model the system through a generalization of the Anderson model. We argue that
this model is exactly solvable when certain constraints are placed upon the dot
Coulomb charging energy, the dot-lead hybridization, and the value of the
applied gate voltage. Using this exact solvability, we access the zero
temperature linear response conductance both in and out of the presence of a
Zeeman field. We are also able to study the finite temperature linear response
conductance. We focus on universal behaviour and identify three primary
features in the transport of the dots: i) a so-called RKKY Kondo effect; ii) a
standard Kondo effect; and iii) interference phenomena leading to sharp
variations in the conductance including conductance zeros. We are able to use
the exact solvability of the dot model to characterize these phenomena
quantitatively. While here we primarily consider a double dot system, the
approach adopted applies equally well to N-dot systems.Comment: 28 pages, 10 figures; references added in v
Boundary Quantum Field Theories with Infinite Resonance States
We extend a recent work by Mussardo and Penati on integrable quantum field
theories with a single stable particle and an infinite number of unstable
resonance states, including the presence of a boundary. The corresponding
scattering and reflection amplitudes are expressed in terms of Jacobian
elliptic functions, and generalize the ones of the massive thermal Ising model
and of the Sinh-Gordon model. In the case of the generalized Ising model we
explicitly study the ground state energy and the one-point function of the
thermal operator in the short-distance limit, finding an oscillating behaviour
related to the fact that the infinite series of boundary resonances does not
decouple from the theory even at very short-distance scales. The analysis of
the generalized Sinh-Gordon model with boundary reveals an interesting
constraint on the analytic structure of the reflection amplitude. The roaming
limit procedure which leads to the Ising model, in fact, can be consistently
performed only if we admit that the nature of the bulk spectrum uniquely fixes
the one of resonance states on the boundary.Comment: 18 pages, 11 figures, LATEX fil
Structure of Psb29/Thf1 and its association with the FtsH protease complex involved in photosystem II repair in cyanobacteria
One strategy for enhancing photosynthesis in crop plants is to improve the ability to repair photosystem II (PSII) in response to irreversible damage by light. D espite the pivotal role of thylakoid embedded FtsH protease complexes in the selective degradation of PSII subunits during repair, little is known about the factors involved in regulating FtsH exp ression. Here we show using the cyanobacterium Synechocystis sp. PCC 6803 that the Psb29 subunit, originally identified as a minor component of His tagged PSII preparations, physically interacts with FtsH complexes in vivo and is required for normal accumulation of the FtsH2/FtsH3 hetero oligo meric complex involved in PSII repair. We show using X ray crystallography that Psb29 from Thermosynechococcus elongatus has a unique fold consisting of a helical bundle and an extended C terminal heli x and contains a highly conserved region that might be involved in binding to FtsH. A similar interaction is likely to occur in Arabidopsis chloroplasts between the Psb29 homologue, termed THF1, and the FTSH2/FTSH5 complex. The direct involvement of Psb29/THF1 in Ft sH accumulation helps explain why THF1 is a target during the hypersensitive response in plants induced by pathogen i nfection. Downregulating FtsH function and the PSII repair cycle via THF1 would cont ribute to the productio
Applications of quantum integrable systems
We present two applications of quantum integrable systems. First, we predict
that it is possible to generate high harmonics from solid state devices by
demostrating that the emission spectrum for a minimally coupled laser field of
frequency to an impurity system of a quantum wire, contains multiples
of the incoming frequency. Second, evaluating expressions for the conductance
in the high temperature regime we show that the caracteristic filling fractions
of the Jain sequence, which occur in the fractional quantum Hall effect, can be
obtained from quantum wires which are described by minimal affine Toda field
theories.Comment: 25 pages of LaTex, 4 figures, based on talk at the 6-th international
workshop on conformal field theories and integrable models, (Chernogolovka,
September 2002
The Scattering Theory of Oscillator Defects in an Optical Fiber
We examine harmonic oscillator defects coupled to a photon field in the
environs of an optical fiber. Using techniques borrowed or extended from the
theory of two dimensional quantum fields with boundaries and defects, we are
able to compute exactly a number of interesting quantities. We calculate the
scattering S-matrices (i.e. the reflection and transmission amplitudes) of the
photons off a single defect. We determine using techniques derived from
thermodynamic Bethe ansatz (TBA) the thermodynamic potentials of the
interacting photon-defect system. And we compute several correlators of
physical interest. We find the photon occupancy at finite temperature, the
spontaneous emission spectrum from the decay of an excited state, and the
correlation functions of the defect degrees of freedom. In an extension of the
single defect theory, we find the photonic band structure that arises from a
periodic array of harmonic oscillators. In another extension, we examine a
continuous array of defects and exactly derive its dispersion relation. With
some differences, the spectrum is similar to that found for EM wave propagation
in covalent crystals. We then add to this continuum theory isolated defects, so
as to obtain a more realistic model of defects embedded in a frequency
dependent dielectric medium. We do this both with a single isolated defect and
with an array of isolated defects, and so compute how the S-matrices and the
band structure change in a dynamic medium.Comment: 32 pages, TeX with harvmac macros, three postscript figure
Interplay of the Scaling Limit and the Renormalization Group: Implications for Symmetry Restoration
Symmetry restoration is usually understood as a renormalization group induced
phenomenon. In this context, the issue of whether one-loop RG equations can be
trusted in predicting symmetry restoration has recently been the subject of
much debate. Here we advocate a more pragmatic point of view and expand the
definition of symmetry restoration to encompass all situations where the
physical properties have only a weak dependence upon an anisotropy in the bare
couplings. Moreover we concentrate on universal properties, and so take a
scaling limit where the physics is well described by a field theory. In this
context, we find a large variety of models that exhibit, for all practical
purposes, symmetry restoration: even if symmetry is not restored in a strict
sense, physical properties are surprisingly insensitive to the remaining
anisotropy.
Although we have adopted an expanded notion of symmetry restoration, we
nonetheless emphasize that the scaling limit also has implications for symmetry
restoration as a renormalization group induced phenomenon. In all the models we
considered, the scaling limit turns out to only permit bare couplings which are
nearly isotropic and small. Then the one-loop beta-function should contain all
the physics and higher loop orders can be neglected. We suggest that this
feature generalizes to more complex models. We exhibit a large class of
theories with current-current perturbations (of which the SO(8) model of
interest in two-leg Hubbard ladders/armchair carbon nanotubes is one) where the
one-loop beta-functions indicates symmetry restoration and so argue that these
results can be trusted within the scaling limit.Comment: 20 pages, 11 figures, RevTe
Form factor expansion for thermal correlators
We consider finite temperature correlation functions in massive integrable
Quantum Field Theory. Using a regularization by putting the system in finite
volume, we develop a novel approach (based on multi-dimensional residues) to
the form factor expansion for thermal correlators. The first few terms are
obtained explicitly in theories with diagonal scattering. We also discuss the
validity of the LeClair-Mussardo proposal.Comment: 41 pages; v2: minor corrections, v3: minor correction
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