16 research outputs found
Determination of the parameters of semiconducting CdF2:In with Schottky barriers from radio-frequency measurements
Physical properties of semiconducting CdF_2 crystals doped with In are
determined from measurements of the radio-frequency response of a sample with
Schottky barriers at frequencies 10 - 10^6 Hz. The dc conductivity, the
activation energy of the amphoteric impurity, and the total concentration of
the active In ions in CdF_2 are found through an equivalent-circuit analysis of
the frequency dependencies of the sample complex impedance at temperatures from
20 K to 300 K. Kinetic coefficients determining the thermally induced
transitions between the deep and the shallow states of the In impurity and the
barrier height between these states are obtained from the time-dependent
radio-frequency response after illumination of the material. The results on the
low-frequency conductivity in CdF_2:In are compared with submillimeter (10^{11}
- 10^{12} Hz) measurements and with room-temperature infrared measurements of
undoped CdF_2. The low-frequency impedance measurements of semiconductor
samples with Schottky barriers are shown to be a good tool for investigation of
the physical properties of semiconductors.Comment: 9 pages, 7 figure
How to Measure Chromo-magnetic Vacuum Background Field in , Hadron-Hadron and Nucleus-Nucleus Collisions
We propose a new type of the measurement which is sensitive to the QCD vacuum
color-magnetic fluctuations: A measure of the axial assymetry of the hadronic
final states produced in the high energy collisions is related to
the chromomagnetic vacuum field strength.Comment: 11 pages,latex,no figures,replaced,final version which takes into
account criticisms of referees of Phys.Rev. Title of the paper was changed.
The formula (14) was corrected, notation in formulae (12) and (13) changed.
Also we added forgotten vectorial notations,corrected misspellings and
improved the style and gramma
Spin Transistor and Quantum Spin Hall Effects in CdBxF2-x - p-CdF2 - CdBxF2-x Sandwich Nanostructures
Planar CdBxF2-x - p-CdF2 - CdBxF2-x sandwich nanostructures prepared on the
surface of the n-type CdF2 bulk crystal are studied to register the spin
transistor and quantum spin Hall effects. The current-voltage characteristics
of the ultra-shallow p+-n junctions verify the CdF2 gap, 7.8 eV, and the
quantum subbands of the 2D holes in the p-type CdF2 quantum well confined by
the CdBxF2-x delta-barriers. The temperature and magnetic field dependencies of
the resistance, specific heat and magnetic susceptibility demonstrate the high
temperature superconductor properties for the CdBxF2-x delta-barriers. The
value of the superconductor energy gap, 102.06 meV, determined by the tunneling
spectroscopy method appears to be in a good agreement with the relationship
between the zero-resistance supercurrent in superconductor state and the
conductance in normal state at the energies of the 2D hole subbands. The
results obtained are evidence of the important role of the multiple Andreev
reflections in the creation of the high spin polarization of the 2D holes in
the edged channels of the sandwich device. The high spin hole polarization in
the edged channels is shown to identify the mechanism of the spin transistor
and quantum spin Hall effects induced by varying the top gate voltage, which is
revealed by the first observation of the Hall quantum conductance staircase.Comment: 5 pages, 9 figure
Elastic and quasi-elastic and scattering in the Dipole Model
We have in earlier papers presented an extension of Mueller's dipole cascade
model, which includes sub-leading effects from energy conservation and running
coupling as well as colour suppressed saturation effects from pomeron loops via
a ``dipole swing''. The model was applied to describe the total and diffractive
cross sections in and collisions, and also the elastic cross
section in scattering.
In this paper we extend the model to describe the corresponding quasi-elastic
cross sections in , namely the exclusive production of vector mesons
and deeply virtual compton scattering. Also for these reactions we find a good
agrement with measured cross sections. In addition we obtain a reasonable
description of the -dependence of the elastic and quasi-elastic
cross sections
Decomposition of the QCD String into Dipoles and Unintegrated Gluon Distributions
We present the perturbative and non-perturbative QCD structure of the
dipole-dipole scattering amplitude in momentum space. The perturbative
contribution is described by two-gluon exchange and the non-perturbative
contribution by the stochastic vacuum model which leads to confinement of the
quark and antiquark in the dipole via a string of color fields. This QCD string
gives important non-perturbative contributions to high-energy reactions. A new
structure different from the perturbative dipole factors is found in the
string-string scattering amplitude. The string can be represented as an
integral over stringless dipoles with a given dipole number density. This
decomposition of the QCD string into dipoles allows us to calculate the
unintegrated gluon distribution of hadrons and photons from the dipole-hadron
and dipole-photon cross section via kT-factorization.Comment: 43 pages, 14 figure
Double spin asymmetry in exclusive rho^0 muoproduction at COMPASS
The longitudinal double spin asymmetry A_1^rho for exclusive leptoproduction
of rho^0 mesons, mu + N -> mu + N + rho, is studied using the COMPASS 2002 and
2003 data. The measured reaction is incoherent exclusive rho^0 production on
polarised deuterons. The Q^2 and x dependence of A_1^rho is presented in a wide
kinematical range: 3x10^-3 < Q^2 < 7 (GeV/c)^2 and 5x10^-5 < x < 0.05. The
presented results are the first measurements of A_1^rho at small Q2 (Q2 < 0.1
(GeV/c)^2) and small x (x < 3x10^-3). The asymmetry is in general compatible
with zero in the whole kinematical range.Comment: 6 Figures, 15 pages, version 2 with updated author list, technical
latex problem fixe