31,715 research outputs found
Nuclear magnetic resonance probes for the Kondo scenario for the 0.7 feature in semiconductor quantum point contact devices
We propose a probe based on nuclear relaxation and Knight shift measurements
for the Kondo scenario for the "0.7 feature" in semiconductor quantum point
contact (QPC) devices. We show that the presence of a bound electron in the QPC
would lead to a much higher rate of nuclear relaxation compared to nuclear
relaxation through exchange of spin with conduction electrons. Furthermore, we
show that the temperature dependence of this nuclear relaxation is very
non-monotonic as opposed to the linear-T relaxation from coupling with
conduction electrons. We present a qualitative analysis for the additional
relaxation due to nuclear spin diffusion (NSD) and study the extent to which
NSD affects the range of validity of our method. The conclusion is that nuclear
relaxation, in combination with Knight shift measurements, can be used to
verify whether the 0.7 feature is indeed due to the presence of a bound
electron in the QPC.Comment: Published version. Appears in a Special Section on the 0.7 Feature
and Interactions in One-Dimensional Systems. 16 page
Stable Topological Superfluid Phase of Ultracold Polar Fermionic Molecules
We show that single-component fermionic polar molecules confined to a 2D
geometry and dressed by a microwave field, may acquire an attractive
dipole-dipole interaction leading to superfluid p-wave pairing at sufficiently
low temperatures even in the BCS regime. The emerging state is the topological
phase promising for topologically protected quantum information
processing. The main decay channel is via collisional transitions to dressed
states with lower energies and is rather slow, setting a lifetime of the order
of seconds at 2D densities cm
Optics with Quantum Hall Skyrmions
A novel type of charged excitation, known as a Skyrmion, has recently been
discovered in quantum Hall systems with filling factor near \nu = 1. A Skyrmion
-- which can be thought of as a topological twist in the spin density of the
electron gas -- has the same charge as an electron, but a much larger spin. In
this review we present a detailed theoretical investigation of the optical
properties of Skyrmions. Our results provide means for the optical detection of
Skyrmions using photoluminescence (PL) spectroscopy. We first consider the
optical properties of Skyrmions in disordered systems. A calculation of the
luminescence energy reveals a special optical signature which allows us to
distinguish between Skyrmions and ordinary electrons. Two experiments to
measure the optical signature are proposed. We then turn to the optical
properties of Skyrmions in pure systems. We show that, just like an ordinary
electron, a Skyrmion may bind with a hole to form a Skyrmionic exciton. The
Skyrmionic exciton can have a lower energy than the ordinary magnetoexciton.
The optical signature of Skyrmions is found to be a robust feature of the PL
spectrum in both disordered and pure systems.Comment: 31 pages, LaTex, 11 eps figures. ijmpb style file included. Review
article submitted to Int. J. Mod. Phys.
Isotope Effect in the Superfluid Density of HTS Cuprates: Stripes, Pseudogap and Impurities
Underdoped cuprates exhibit a normal-state pseudogap, and their spins and
doped carriers tend to spatially separate into 1- or 2-D stripes. Some view
these as central to superconductivity, others as peripheral and merely
competing. Using LaSrCuZnO we show that an oxygen
isotope effect in and in the superfluid density can be used to
distinguish between the roles of stripes and pseudogap and also to detect the
presence of impurity scattering. We conclude that stripes and pseudogap are
distinct, and both compete and coexist with superconductivity.Comment: Revised submission to PRL with added appendix on a possible isotope
effect in the effective mass, 4 pages, 3 figure
Improved +He potentials by inversion, the tensor force and validity of the double folding model
Improved potential solutions are presented for the inverse scattering problem
for +He data. The input for the inversions includes both the data of
recent phase shift analyses and phase shifts from RGM coupled-channel
calculations based on the NN Minnesota force. The combined calculations provide
a more reliable estimate of the odd-even splitting of the potentials than
previously found, suggesting a rather moderate role for this splitting in
deuteron-nucleus scattering generally. The approximate parity-independence of
the deuteron optical potentials is shown to arise from the nontrivial
interference between antisymmetrization and channel coupling to the deuteron
breakup channels. A further comparison of the empirical potentials established
here and the double folding potential derived from the M3Y effective NN force
(with the appropriate normalisation factor) reveals strong similarities. This
result supports the application of the double folding model, combined with a
small Majorana component, to the description even of such a loosely bound
projectile as the deuteron. In turn, support is given for the application of
iterative-perturbative inversion in combination with the double folding model
to study fine details of the nucleus-nucleus potential. A -He tensor
potential is also derived to reproduce correctly the negative Li quadrupole
moment and the D-state asymptotic constant.Comment: 22 pages, 12 figures, in Revte
Vehicle/engine integration
VEHICLE/ENGINE Integration Issues are explored for orbit transfer vehicles (OTV's). The impact of space basing and aeroassist on VEHICLE/ENGINE integration is discussed. The AOTV structure and thermal protection subsystem weights were scaled as the vehicle length and surface was changed. It is concluded that for increased allowable payload lengths in a ground-based system, lower length-to-diameter (L/D) is as important as higher mixture ration (MR) in the range of mid L/D ATOV's. Scenario validity, geometry constraints, throttle levels, reliability, and servicing are discussed in the context of engine design and engine/vehicle integration
Quantum and classical surface acoustic wave induced magnetoresistance oscillations in a 2D electron gas
We study theoretically the geometrical and temporal commensurability
oscillations induced in the resistivity of 2D electrons in a perpendicular
magnetic field by surface acoustic waves (SAWs). We show that there is a
positive anisotropic dynamical classical contribution and an isotropic
non-equilibrium quantum contribution to the resistivity. We describe how the
commensurability oscillations modulate the resonances in the SAW-induced
resistivity at multiples of the cyclotron frequency. We study the effects of
both short-range and long-range disorder on the resistivity corrections for
both the classical and quantum non-equilibrium cases. We predict that the
quantum correction will give rise to zero-resistance states with associated
geometrical commensurability oscillations at large SAW amplitude for
sufficiently large inelastic scattering times. These zero resistance states are
qualitatively similar to those observed under microwave illumination, and their
nature depends crucially on whether the disorder is short- or long-range.
Finally, we discuss the implications of our results for current and future
experiments on two dimensional electron gases.Comment: 16 pages, 8 figure
'I-I' and 'I-me' : Transposing Buber's interpersonal attitudes to the intrapersonal plane
Hermans' polyphonic model of the self proposes that dialogical relationships can be established between multiple I-positions1 (e.g., Hermans, 2001a). There have been few attempts, however, to explicitly characterize the forms that these intrapersonal relationships may take. Drawing on Buber's (1958) distinction between the 'I-Thou' and 'I-It' attitude, it is proposed that intrapersonal relationships can take one of two forms: an 'I-I' form, in which one I-position encounters and confirms another I-position in its uniqueness and wholeness; and an 'I-Me' form, in which one I-position experiences another I-position in a detached and objectifying way. This article argues that this I-Me form of intrapersonal relating is associated with psychological distress, and that this is so for a number of reasons: Most notably, because an individual who objectifies and subjugates certain I-position cannot reconnect with more central I-positions when dominance reversal (Hermans, 2001a) takes place. On this basis, it is suggested that a key role of the therapeutic process is to help clients become more able to experience moments of I-I intrapersonal encounter, and it is argued that this requires the therapist to confirm the client both as a whole and in terms of each of his or her different voices
The Response to a Perturbation in the Reflection Amplitude
We apply inverse scattering theory to calculate the functional derivative of
the potential and wave function of a one-dimensional
Schr\"odinger operator with respect to the reflection amplitude .Comment: 16 pages, no figure
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