5,032 research outputs found
Interplay between Kondo physics and spin-orbit coupling in carbon nanotube quantum dots
We investigate the influence of spin-orbit coupling on the Kondo effects in
carbon nanotube quantum dots, using the numerical renormalization group
technique. A sufficiently large spin-orbit coupling is shown to destroy the
SU(4) Kondo effects at zero magnetic field, leaving only two SU(2) Kondo
effects in the one- and three-electron Coulomb blockade valleys. On applying a
finite magnetic field, two additional, spin-orbit induced SU(2) Kondo effects
arise in the three- and two-electron valleys. Using physically realistic model
parameters, we calculate the differential conductance over a range of gate
voltages, temperatures and fields. The results agree well with measurements
from two different experimental devices in the literature, and explain a number
of observations that are not described within the standard framework of the
SU(4) Anderson impurity model.Comment: 15 pages, 11 figure
A Practical Guide to Operator/ Surface-Owner Disputes and the Current State of the Accommodation Doctrine
This Article provides an overview of the operator\u27s rights and a practical guide to the procedures available to enforce them. Of particular emphasis, this Article will discuss how an operator can use injunctive relief to prevent surface-owner interference, and will specifically provide a checklist of sorts for how an operator can obtain a temporary restraining order. This Article will also address how the operator\u27s rights can be limited by the accommodation doctrine. In this regard, this Article will examine how the accommodation doctrine is triggered, what the surface owner must prove when asserting the accommodation doctrine, and whether the accommodation doctrine provides a mechanism for the surface owner to recover damages from the operator for unreasonable surface use
Field-dependent dynamics of the Anderson impurity model
Single-particle dynamics of the Anderson impurity model in the presence of a
magnetic field are considered, using a recently developed local moment
approach that encompasses all energy scales, field and interaction strengths.
For strong coupling in particular, the Kondo scaling regime is recovered. Here
the frequency () and field ()
dependence of the resultant universal scaling spectrum is obtained in large
part analytically, and the field-induced destruction of the Kondo resonance
investigated. The scaling spectrum is found to exhibit the slow logarithmic
tails recently shown to dominate the zero-field scaling spectrum. At the
opposite extreme of the Fermi level, it gives asymptotically exact agreement
with results for statics known from the Bethe ansatz. Good agreement is also
found with the frequency and field-dependence of recent numerical
renormalization group calculations. Differential conductance experiments on
quantum dots in the presence of a magnetic field are likewise considered; and
appear to be well accounted for by the theory. Some new exact results for the
problem are also established
Application of random coherence order selection in gradient-enhanced multidimensional NMR
Development of multidimensional NMR is essential to many applications, for example in high resolution structural studies of biomolecules. Multidimensional techniques enable separation of NMR signals over several dimensions, improving signal resolution, whilst also allowing identification of new connectivities. However, these advantages come at a significant cost. The Fourier transform theorem requires acquisition of a grid of regularly spaced points to satisfy the Nyquist criterion, while frequency discrimination and acquisition of a pure phase spectrum require acquisition of both quadrature components for each time point in every indirect (non-acquisition) dimension, adding a factor of 2 to the number of free-induction decays which must be acquired, where is the number of dimensions. Compressed sensing (CS) ℓ-norm minimisation in combination with non-uniform sampling (NUS) has been shown to be extremely successful in overcoming the Nyquist criterion. Previously, maximum entropy reconstruction has also been used to overcome the limitation of frequency discrimination, processing data acquired with only one quadrature component at a given time interval, known as random phase detection (RPD), allowing a factor of two reduction in the number of points for each indirect dimension (Maciejewski et al. 2011 108 16640). However, whilst this approach can be easily applied in situations where the quadrature components are acquired as amplitude modulated data, the same principle is not easily extended to phase modulated (P-/N-type) experiments where data is acquired in the form exp () or exp (−), and which make up many of the multidimensional experiments used in modern NMR. Here we demonstrate a modification of the CS ℓ-norm approach to allow random coherence order selection (RCS) for phase modulated experiments; we generalise the nomenclature for RCS and RPD as random quadrature detection (RQD). With this method, the power of RQD can be extended to the full suite of experiments available to modern NMR spectroscopy, allowing resolution enhancements for all indirect dimensions; alone or in combination with NUS, RQD can be used to improve experimental resolution, or shorten experiment times, of considerable benefit to the challenging applications undertaken by modern NMR.This is the final version of the article. It first appeared from IOP Publishing via http://dx.doi.org/10.1088/1742-6596/699/1/01200
Local quantum phase transition in the pseudogap Anderson model: scales, scaling and quantum critical dynamics
The pseudogap Anderson impurity model provides a paradigm for understanding
local quantum phase transitions, in this case between generalised fermi liquid
and degenerate local moment phases. Here we develop a non-perturbative local
moment approach to the generic asymmetric model, encompassing all energy scales
and interaction strengths and leading thereby to a rich description of the
problem. We investigate in particular underlying phase boundaries, the critical
behaviour of relevant low-energy scales, and single-particle dynamics embodied
in the local spectrum. Particular attention is given to the resultant universal
scaling behaviour of dynamics close to the transition in both the GFL and LM
phases, the scale-free physics characteristic of the quantum critical point
itself, and the relation between the two.Comment: 39 pages, 19 figure
Inhibition of thoughts and actions in obsessive-compulsive disorder: extending the endophenotype?
Original article can be found at: http://journals.cambridge.org/ Copyright © Cambridge University Press 2009 The online version of this article is published within an Open Access environment subject to the conditions of the Creative Commons Attribution-NonCommercial-ShareAlike licence <http://creativecommons.org/licenses/by-nc-sa/2.5/>.Background: Obsessive-compulsive disorder (OCD) has been associated with impairments in stop-signal inhibition, a measure of motor response suppression. The study used a novel paradigm to examine both thought suppression and response inhibition in OCD, where the modulatory effects of stimuli relevant to OCD could also be assessed. Additionally, the study compared inhibitory impairments in OCD patients with and without co-morbid depression, as depression is the major co-morbidity of OCD. Method: Volitional response suppression and unintentional thought suppression to emotive and neutral stimuli were examined using a novel thought stop-signal task. The thought stop-signal task was administered to non-depressed OCD patients, depressed OCD patients and healthy controls (n=20 per group). Results: Motor inhibition impairments were evident in OCD patients, while motor response performance did not differ between patients and controls. Switching to a new response but not motor inhibition was affected by stimulus relevance in OCD patients. Additionally, unintentional thought suppression as measured by repetition priming was intact. OCD patients with and without depression did not differ on any task performance measures, though there were significant differences in all self-reported measures. Conclusions: Results support motor inhibition deficits in OCD that remain stable regardless of stimulus meaning or co-morbid depression. Only switching to a new response was influenced by stimulus meaning. When response inhibition was successful in OCD patients, so was the unintentional suppression of the accompanying thought.Peer reviewe
Letters from Wm. Chas. Roberts, J. B. Fisher, A. H. Throckmorton, Lucien Waggener, J. W. Logan, and A. B. Nelson
Letters of recommendation for O. W. Long
Axiomatic geometrical optics, Abraham-Minkowski controversy, and photon properties derived classically
By restating geometrical optics within the field-theoretical approach, the
classical concept of a photon (and, more generally, any elementary excitation)
in arbitrary dispersive medium is introduced, and photon properties are
calculated unambiguously. In particular, the canonical and kinetic momenta
carried by a photon, as well as the two corresponding energy-momentum tensors
of a wave, are derived from first principles of Lagrangian mechanics. As an
example application of this formalism, the Abraham-Minkowski controversy
pertaining to the definitions of these quantities is resolved for linear waves
of arbitrary nature, and corrections to the traditional formulas for the photon
kinetic energy-momentum are found. Several other applications of axiomatic
geometrical optics to electromagnetic waves are also presented
Symmetric Anderson impurity model with a narrow band
The single channel Anderson impurity model is a standard model for the
description of magnetic impurities in metallic systems. Usually, the bandwidth
represents the largest energy scale of the problem. In this paper, we analyze
the limit of a narrow band, which is relevant for the Mott-Hubbard transition
in infinite dimensions. For the symmetric model we discuss two different
effects: i) The impurity contribution to the density of states at the Fermi
surface always turns out to be negative in such systems. This leads to a new
crossover in the thermodynamic quantities that we investigate using the
numerical renormalization group. ii) Using the Lanczos method, we calculate the
impurity spectral function and demonstrate the breakdown of the skeleton
expansion on an intermediate energy scale. Luttinger's theorem, as an example
of the local Fermi liquid property of the model, is shown to still be valid.Comment: 4 pages RevTeX, 2 eps figures included, final versio
- …