21,679 research outputs found
Relativistic free-particle quantization on the light-front: New aspects
We use the light-front machinery to study the behavior of a relativistic free
particle and obtain the quantum commutation relations from the classical
Poisson brackets. We argue that the usual projection onto the light-front
coordinates for these from the covariant commutation ralations does not
reproduce the expected results.Comment: To appear in the proceedings "IX Hadron Physics and VII Relativistic
Aspects of Nuclear Physics: A Joint Meeting on QCD and QGP, Hadron
Physics-RANP,2004,Angra dos Reis, Rio de Janeiro,Brazi
Surprises in the relativistic free-particle quantization on the light-front
We use the light front ``machinery'' to study the behavior of a relativistic
free particle and obtain the quantum commutation relations from the classical
Poisson brackets. We argue that their usual projection onto the light-front
coordinates from the covariant commutation relations show that there is an
inconsistency in the expected correlation between canonically conjugate
variables ``time'' and ``energy''. Moreover we show that this incompatibility
originates from the very definition of the Poisson brackets that is employed
and present a simple remedy to this problem and envisages a profound physical
implication on the whole process of quantization.Comment: 13 page
Ultraviolet Behavior of the Gluon Propagator in the Maximal Abelian Gauge
The ultraviolet asymptotic behavior of the gluon propagator is evaluated in
the maximal Abelian gauge in the SU(2) gauge theory on the basis of the
renormalization-group improved perturbation theory at the one-loop level.
Square-root singularities obtained in the Euclidean domain are attributed to
artifacts of the one-loop approximation in the maximal Abelian gauge and the
standard normalization condition for the propagator used in our study. It is
argued that this gauge is essentially nonperturbative.Comment: 15 pages, 2 figure
The dilute A_L models and the integrable perturbations of unitary minimal CFTs
Recently, a set of thermodynamic Bethe ansatz equations is proposed by Dorey,
Pocklington and Tateo for unitary minimal models perturbed by \phi_{1,2} or
\phi_{2,1} operator. We examine their results in view of the lattice analogues,
dilute A_L models at regime 1 and 2. Taking M_{5,6}+\phi_{1,2} and
M_{3,4}+\phi_{2,1} as the simplest examples, we will explicitly show that the
conjectured TBA equations can be recovered from the lattice model in a scaling
limit.Comment: 14 pages, 2 figure
Electrical transport and ferromagnetism in Ga1-xMnxAs synthesized by ion implantation and pulsed-laser melting
We present a detailed investigation of the magnetic and magnetotransport
properties of thin films of ferromagnetic Ga1-xMnxAs synthesized using ion
implantation and pulsed-laser melting (II-PLM). The field and
temperature-dependent magnetization, magnetic anisotropy, temperature-dependent
resistivity, magnetoresistance, and Hall effect of II-PLM Ga1-xMnxAs films have
all of the characteristic signatures of the strong p-d interaction of holes and
Mn ions observed in the dilute hole-mediated ferromagnetic phase. The
ferromagnetic and electrical transport properties of II-PLM films correspond to
the peak substitutional Mn concentration meaning that the non-uniform Mn depth
distribution is unimportant in determining the film properties. Good
quantitative agreement is found with films grown by low temperature molecular
beam epitaxy (LT-MBE) and having the similar substitutional Mn_Ga composition.
Additionally, we demonstrate that II-PLM Ga1-xMnxAs films are free from
interstitial Mn_I because of the high temperature processing. At high Mn
implantation doses the kinetics of solute redistribution during solidification
alone determine the maximum resulting Mn_Ga concentration. Uniaxial anisotropy
between in-plane [-110]and [110] directions is present in II-PLM Ga1-xMnxAs
giving evidence for this being an intrinsic property of the carrier-mediated
ferromagnetic phase
Low energy n-\nuc{3}{H} scattering : a novel testground for nuclear interaction
The low energy n-\nuc{3}{H} elastic cross sections near the resonance peak
are calculated by solving the 4-nucleon problem with realistic NN interactions.
Three different methods -- Alt, Grassberger and Shandas (AGS), Hyperspherical
Harmonics and Faddeev-Yakubovsky -- have been used and their respective results
are compared. We conclude on a failure of the existing NN forces to reproduce
the n-\nuc{3}{H} total cross section.Comment: To be published in Phys. Rev.
Detection of Neutron Scattering from Phase IV of Ce0.7La0.3B6: A Confirmation of the Octupole Order
We have performed a single crystal neutron scattering experiment on
Ce0.7La0.3B6 to investigate the order parameter of phase IV microscopically.
Below the phase transition temperature 1.5 K of phase IV, weak but distinct
superlattice reflections at the scattering vector (h/2,h/2,l/2) (h, l = odd
number) have been observed by neutron scattering for the first time. The
intensity of the superlattice reflections is stronger for high scattering
vectors, which is quite different from the usual magnetic form factor of
magnetic dipoles. This result directly evidences that the order parameter of
phase IV has a complex magnetization density, consistent with the recent
experimental and theoretical prediction in which the order parameter is the
magnetic octupoles Tbeta with Gamma5 symmetry of point group Oh. Neutron
scattering experiments using short wavelength neutrons, as done in this study,
could become a general method to study the high-rank multipoles in f electron
systems.Comment: 4 pages, 4 figure
Fowler-Nordheim-like local injection of photoelectrons from a silicon tip
Tunneling between a photo-excited p-type silicon tip and a gold surface is
studied as a function of tip bias, tip/sample distance and light intensity. In
order to extend the range of application of future spin injection experiments,
the measurements are carried out under nitrogen gas at room temperature. It is
found that while tunneling of valence band electrons is described by a standard
process between the semiconductor valence band and the metal, the tunneling of
photoelectrons obeys a Fowler-Nordheim-like process directly from the
conduction band. In the latter case, the bias dependence of the photocurrent as
a function of distance is in agreement with theoretical predictions which
include image charge effects. Quantitative analysis of the bias dependence of
the dark and photocurrent spectra gives reasonable values for the distance, and
for the tip and metal work functions. For small distances image charge effects
induce a vanishing of the barrier and the bias dependence of the photocurrent
is exponential. In common with many works on field emission, fluctuations in
the tunneling currents are observed. These are mainly attributed to changes in
the prefactor for the tunneling photocurrent, which we suggest is caused by an
electric-field-induced modification of the thickness of the natural oxide layer
covering the tip apex.Comment: 12 pages, 11 figures. Submitted to Phys. Rev.
Energy levels in polarization superlattices: a comparison of continuum strain models
A theoretical model for the energy levels in polarization superlattices is
presented. The model includes the effect of strain on the local
polarization-induced electric fields and the subsequent effect on the energy
levels. Two continuum strain models are contrasted. One is the standard strain
model derived from Hooke's law that is typically used to calculate energy
levels in polarization superlattices and quantum wells. The other is a
fully-coupled strain model derived from the thermodynamic equation of state for
piezoelectric materials. The latter is more complete and applicable to strongly
piezoelectric materials where corrections to the standard model are
significant. The underlying theory has been applied to AlGaN/GaN superlattices
and quantum wells. It is found that the fully-coupled strain model yields very
different electric fields from the standard model. The calculated intersubband
transition energies are shifted by approximately 5 -- 19 meV, depending on the
structure. Thus from a device standpoint, the effect of applying the
fully-coupled model produces a very measurable shift in the peak wavelength.
This result has implications for the design of AlGaN/GaN optical switches.Comment: Revtex
Quadrupolar Kondo Effect in Non-Kramers Doublet System PrInAg2
We performed ultrasonic measurement on the rare-earth intermetallic compound
PrInAg_2 to examine the quadrupolar Kondo effect associated with the
non-Kramers Gamma_3 doublet ground state. The characteristic softening of the
elastic constant (c_{11}-c_{12})/2 below 10 K in PrInAg_2 is attributed to a
Curie term in quadrupolar susceptibility for the quadrupole O_2^2=J_x^2-J_y^2
of the stable Gamma_3 ground state. (c_{11}-c_{12})/2 turns to a slight
increase with the -lnT dependence below 0.1 K, which suggests the quenching of
the quadrupolar moment in the quadrupolar Kondo state. Under applied magnetic
fields of 10 T and 15 T above 8.7 T corresponding to the Kondo temperature T_K
of ~ 0.86 K, the behavior of (c_{11}-c_{12})/2 is described in terms of
quadrupolar susceptibility for the stable 4f^2 state.Comment: PDF, 10pages + 5figures, Strongly Correlated Electron
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