10,348 research outputs found
Edge Electron Gas
The uniform electron gas, the traditional starting point for density-based
many-body theories of inhomogeneous systems, is inappropriate near electronic
edges. In its place we put forward the appropriate concept of the edge electron
gas.Comment: 4 pages RevTex with 7 ps-figures included. Minor changes in
title,text and figure
Voltage Control of Exchange Coupling in Phosphorus Doped Silicon
Motivated by applications to quantum computer architectures we study the
change in the exchange interaction between neighbouring phosphorus donor
electrons in silicon due to the application of voltage biases to surface
control electrodes. These voltage biases create electro-static fields within
the crystal substrate, perturbing the states of the donor electrons and thus
altering the strength of the exchange interaction between them. We find that
control gates of this kind can be used to either enhance, or reduce the
strength of the interaction, by an amount that depends both on the magnitude
and orientation of the donor separation.Comment: 5 Pages, 5 Figure
Optically induced spin to charge transduction in donor spin read-out
The proposed read-out configuration D+D- for the Kane Si:P
architecture[Nature 393, 133 (1998)] depends on spin-dependent electron
tunneling between donors, induced adiabatically by surface gates. However,
previous work has shown that since the doubly occupied donor state is so
shallow the dwell-time of the read-out state is less than the required time for
measurement using a single electron transistor (SET). We propose and analyse
single-spin read-out using optically induced spin to charge transduction, and
show that the top gate biases, required for qubit selection, are significantly
less than those demanded by the Kane scheme, thereby increasing the D+D-
lifetime. Implications for singlet-triplet discrimination for electron spin
qubits are also discussed.Comment: 8 pages, 10 figures; added reference, corrected typ
Probing the band structure of quadri-layer graphene with magneto-phonon resonance
We show how the magneto-phonon resonance, particularly pronounced in sp2
carbon allotropes, can be used as a tool to probe the band structure of
multilayer graphene specimens. Even when electronic excitations cannot be
directly observed, their coupling to the E2g phonon leads to pronounced
oscillations of the phonon feature observed through Raman scattering
experiments with multiple periods and amplitudes detemined by the electronic
excitation spectrum. Such experiment and analysis have been performed up to 28T
on an exfoliated 4-layer graphene specimen deposited on SiO2, and the observed
oscillations correspond to the specific AB stacked 4-layer graphene electronic
excitation spectrum.Comment: 11 pages, 5 Fi
Linking entanglement and quantum phase transitions via density functional theory
Density functional theory (DFT) is shown to provide a novel conceptual and
computational framework for entanglement in interacting many-body quantum
systems. DFT can, in particular, shed light on the intriguing relationship
between quantum phase transitions and entanglement. We use DFT concepts to
express entanglement measures in terms of the first or second derivative of the
ground state energy. We illustrate the versatility of the DFT approach via a
variety of analytically solvable models. As a further application we discuss
entanglement and quantum phase transitions in the case of mean field
approximations for realistic models of many-body systems.Comment: 6 pages, 2 figure
Immigration, obesity and labor market outcomes in the UK
We estimate the dual effects of immigration and obesity on labor market outcomes in the UK. There is only one other paper that has estimated these dual effects on a sample of immigrants to the US. We use the British Household Panel Survey, which contains information on height and weight for 2004 and 2006, along with immigration status and labor market outcomes. This was a period of increased immigration to the UK resulting in large part from the accession of new EU member states, though our sample includes both recent arrivals and those who have been in the UK for decades. We first analyze an immigrant-only sample and then expand the sample to compare the experience of these immigrants to natives with similar weight and other observable characteristics. We find support for the healthy immigrant hypothesis that suggests that immigrants are less likely to be obese than natives, and also evidence of an assimilation effect in which immigrants' weight increases with their time in the UK. The results indicate a wage premium and higher proportions of white collar work for immigrant men, but a wage penalty and lower proportions of white collar work for overweight and obese immigrant men. We find weaker but still negative associations between weight and labor market outcomes for immigrant women. Data limitations preclude efforts to address endogeneity, so these findings should be viewed as associations that support the need for better data for additional analysis of the dual effects of immigration and obesity on labor market outcomes
Optical beam guidance in monolithic polymer chips for miniaturized colorimetric assays
For the first time, we present a simple and robust optical concept to enable precise and sensitive read-out of colorimetric assays in flat lab-on-a-chip devices. The optical guidance of the probe beam through an incorporated measurement chamber to the detector is based on the total internal reflection at V-grooves in the polymer chip. This way, the optical path length through the flat measurement chamber and thus the performance of the measurements are massively enhanced compared to direct (perpendicular) beam incidence. This is demonstrated by a chip-based, colorimetric glucose-assay on serum. Outstanding features are an excellent reproducibility (CV= 1.91 %), a competitive lower limit of detection (cmin = 124 μM), and a high degree of linearity (R2 = 0.998) within a working range extending over nearly three orders of magnitude
Total energy global optimizations using non orthogonal localized orbitals
An energy functional for orbital based calculations is proposed, which
depends on a number of non orthogonal, localized orbitals larger than the
number of occupied states in the system, and on a parameter, the electronic
chemical potential, determining the number of electrons. We show that the
minimization of the functional with respect to overlapping localized orbitals
can be performed so as to attain directly the ground state energy, without
being trapped at local minima. The present approach overcomes the multiple
minima problem present within the original formulation of orbital based
methods; it therefore makes it possible to perform calculations for an
arbitrary system, without including any information about the system bonding
properties in the construction of the input wavefunctions. Furthermore, while
retaining the same computational cost as the original approach, our formulation
allows one to improve the variational estimate of the ground state energy, and
the energy conservation during a molecular dynamics run. Several numerical
examples for surfaces, bulk systems and clusters are presented and discussed.Comment: 24 pages, RevTex file, 5 figures available upon reques
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