8,000 research outputs found
Polarization-preserving confocal microscope for optical experiments in a dilution refrigerator with high magnetic field
We present the design and operation of a fiber-based cryogenic confocal
microscope. It is designed as a compact cold-finger that fits inside the bore
of a superconducting magnet, and which is a modular unit that can be easily
swapped between use in a dilution refrigerator and other cryostats. We aimed at
application in quantum optical experiments with electron spins in
semiconductors and the design has been optimized for driving with, and
detection of optical fields with well-defined polarizations. This was
implemented with optical access via a polarization maintaining fiber together
with Voigt geometry at the cold finger, which circumvents Faraday rotations in
the optical components in high magnetic fields. Our unit is versatile for use
in experiments that measure photoluminescence, reflection, or transmission, as
we demonstrate with a quantum optical experiment with an ensemble of
donor-bound electrons in a thin GaAs film.Comment: 9 pages, 7 figure
Electromagnetically Induced Transparency with an Ensemble of Donor-Bound Electron Spins in a Semiconductor
We present measurements of electromagnetically induced transparency with an
ensemble of donor- bound electrons in low-doped n-GaAs. We used optical
transitions from the Zeeman-split electron spin states to a bound trion state
in samples with optical densities of 0.3 and 1.0. The electron spin dephasing
time T* \approx 2 ns was limited by hyperfine coupling to fluctuating nuclear
spins. We also observe signatures of dynamical nuclear polarization, but find
these effects to be much weaker than in experiments that use electron spin
resonance and related experiments with quantum dots.Comment: 4 pages, 4 figures; Improved analysis of data in Fig. 3, corrected
factors of 2 and p
Fine structure splittings of excited P and D states in charmonium
It is shown that the fine structure splittings of the and
excited states in charmonium are as large as those of the state if the
same is used. The predicted mass
GeV appears to be 120 MeV lower that the center of gravity of the
multiplet and lies below the threshold. Our value of
is approximately 80 MeV lower than that from the paper by Godfrey and Isgur
while the differences in the other masses are \la 20 MeV. Relativistic
kinematics plays an important role in our analysis.Comment: 12 page
Long-range potential fluctuations and 1/f noise in hydrogenated amorphous silicon
We present a microscopic theory of the low-frequency voltage noise (known as
"1/f" noise) in micrometer-thick films of hydrogenated amorphous silicon. This
theory traces the noise back to the long-range fluctuations of the Coulomb
potential produced by deep defects, thereby predicting the absolute noise
intensity as a function of the distribution of defect activation energies. The
predictions of this theory are in very good agreement with our own experiments
in terms of both the absolute intensity and the temperature dependence of the
noise spectra.Comment: 8 pages, 3 figures, several new parts and one new figure are added,
but no conceptual revision
Leptonic widths of high excitations in heavy quarkonia
Agreement with the measured electronic widths of the ,
, and resonances is shown to be reached if two
effects are taken into account: a flattening of the confining potential at
large distances and a total screening of the gluon-exchange interaction at
r\ga 1.2 fm. The leptonic widths of the unobserved and
resonances: keV and
keV are predicted.Comment: 11 pages revtex
The highly polarized open cluster Trumpler 27
We have carried out multicolor linear polarimetry (UBVRI) of the brightest
stars in the area of the open cluster Trumpler 27. Our data show a high level
of polarization in the stellar light with a considerable dispersion, from to . The polarization vectors of the cluster members appear to be
aligned. Foreground polarization was estimated from the data of some non-member
objects, for which two different components were resolved: the first one
associated with a dust cloud close to the Sun producing
and degrees, and a second component, the main source of
polarization for the cluster members, originated in another dust cloud, which
polarizes the light in the direction of degrees. From a detailed
analysis, we found that the two components have associated values for the first one, and for the other. Due the
difference in the orientation of both polarization vectors, almost 90 degrees
(180 degrees at the Stokes representation), the first cloud (
degrees) depolarize the light strongly polarized by the second one ( degrees).Comment: 12 Pages, 6 Figures, 2 tables (9 Pages), accepted for publication in
A
Neutron Scattering Study on Competition between Hidden Order and Antiferromagnetism in U(Ru_{1-x}Rh_x)_2Si_2 (x <= 0.05)
We have performed elastic and inelastic neutron scattering experiments on the
solid solutions U(Ru_{1-x}Rh_x)_2Si_2 for the Ru rich concentrations: x=0,
0.01, 0.02, 0.025, 0.03, 0.04 and 0.05. Hidden order is suppressed with
increasing x, and correspondingly the onset temperature T_m (~ 17.5 K at x=0)
of weak antiferromagnetic (AF) Bragg reflection decreases. For x=0.04 and 0.05,
no magnetic order is detected in the investigated temperature range down to 1.4
K. In the middle range, 0.02 <= x <= 0.03, we found that the AF Bragg
reflection is strongly enhanced. At x=0.02, this takes place at ~ 7.7 K (=T_M),
which is significantly lower than T_m (~ 13.7 K). T_M increases with increasing
x, and seems to merge with T_m at x=0.03. If the AF state is assumed to be
homogeneous, the staggered moment \mu_o estimated at 1.4 K increases from
0.02(2) \mu_B/U (x=0) to 0.24(1) \mu_B/U (x=0.02). The behavior is similar to
that observed under hydrostatic pressure (\mu_o increases to ~ 0.25 \mu_B/U at
1.0 GPa), suggesting that the AF evolution induced by Rh doping is due to an
increase in the AF volume fraction. We also found that the magnetic excitation
observed at Q=(1,0,0) below T_m disappears as T is lowered below T_M.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
The relationship of offending style to psychological and social risk factors in a sample of adolescent males
Research has indicated that life-course persistent offenders typically vary their offending style, following a criminal career progression from co to solo offending. Few studies have investigated the offenders who contemporaneously mix their style of offending. A sample of 1047 male adolescent offenders from the Pathways to Desistance study was investigated over a seven-year period. Participants were identified as solo, co or contemporaneous mixed style (CMS) offenders for each wave of data and one-way between groups analysis of variance was conducted to examine variations between the different offending styles in terms of offending frequencies, exposure to violence, peer antisocial behaviour and influence, resistance to peer influence, impulse control, and psychopathy. CMS offenders were found to consistently report significantly higher rates of offending and present significantly higher negative risk factors and lower protective risk factors than solo and co offenders for the duration of the study. A Multinomial Logistic Regression was used to investigate predictors of offending style with CMS as the reference category. Higher levels of exposure to violence and peer antisocial behaviour and lower levels of impulse control predicted membership of the CMS group for the first part of the study when compared with co-offenders; and higher levels of exposure to violence and peer antisocial behaviour continued to predict CMS offending when compared to solo offenders until the end of the study
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