990 research outputs found
Chiral spin currents and spectroscopically accessible single merons in quantum dots
We provide unambiguous theoretical evidence for the formation of
correlation-induced isolated merons in rotationally-symmetric quantum dots. Our
calculations rely on neither the lowest-Landau-level approximation, nor on the
maximum-density-droplet approximation, nor on the existence of a spin-polarized
state. For experimentally accessible system parameters, unbound merons condense
in the ground state at magnetic fields as low as T and for as few
as N = 3 confined fermions. The four-fold degenerate ground-state at
corresponds to four orthogonal merons characterized by their
topological chirality and charge . This degeneracy is lifted by the
Rashba and Dresselhaus spin-orbit interaction, which we include perturbatively,
yielding spectroscopic accessibility to individual merons. We further derive a
closed-form expression for the topological chirality in the form of a chiral
spin current and use it to both characterize our states and predict the
existence of other topological textures in other regions of phase space, for
example, at N=5. Finally, we compare the spin textures of our numerically exact
meron states to ansatz wave-functions of merons in quantum Hall droplets and
find that the ansatz qualitatively describes the meron states.Comment: 4 pages, 5 figures; minor title change, typos fixe
Complex Response Function of Magnetic Resonance Spectrometers
A vectorial analysis of magnetic resonance spectrometers, based on traveling
wave resonators and including the reference arm and the automatic control of
frequency, has been developed. The proposed model, valid also for stationary
wave resonators, gives the response function of the spectrometer for any
working condition, including scalar detectors with arbitrary response law and
arbitrary excitation frequency. The purely dispersive and purely absorptive
linear responses are discussed in detail for different scalar detectors. The
developed approach allows for optimizing the performances of the spectrometer
and for obtaining the intrinsic lineshape of the sample in a very broad range
of working conditions. More complex setups can be modeled following the
proposed scheme.Comment: PDF Acrobat 4.0 file, 15 pages, 2 figures, revised version with added
reference and corrected typo
Multiple superconducting transitions in the Sr3Ru2O7 region of Sr3Ru2O7-Sr2RuO4 eutectic crystals
We report superconducting properties of Sr3Ru2O7-Sr2RuO4 eutectic crystals,
consisting of the spin-triplet superconductor Sr2RuO4 with a monolayer stacking
of RuO2 planes and the metamagnetic normal metal Sr3Ru2O7 with a bilayer
stacking. Although Sr3Ru2O7 has not been reported to exhibit superconductivity
so far, our AC susceptibility measurements revealed multiple superconducting
transitions occurring in the Sr3Ru2O7 region of the eutectic crystals. The
diamagnetic shielding essentially reached the full fraction at low AC fields
parallel to the c axis. However, both the shielding fraction and the onset
temperature are easily suppressed by AC fields of larger than 0.1 mT-rms and no
anomaly was observed in the specific heat. Moreover, the critical field curves
of these transitions have a positive curvature near zero fields, which is
different from the upper critical field curve of the bulk Sr2RuO4. These facts
suggest that the superconductivity observed in the Sr3Ru2O7 region is not a
bulk property. To explain these experimental results, we propose the scenario
that stacking RuO2 planes, the building block of superconducting Sr2RuO4, are
contained in the Sr3Ru2O7 region as stacking faults.Comment: 8 pages, 10 figures, accepted for publication in Phys. Rev.
Tadalafil modulates aromatase activity and androgen receptor expression in a human osteoblastic cell in vitro model
Purpose Phosphodiesterase type-5 inhibitor (PDE5i)
tadalafil administration in men with erectile dysfunction is
associated with increased testosterone/estradiol ratio, leading
to hypothesize a potential increased effect of androgen
action on target tissues. We aimed to characterize, in a cellular
model system in vitro, the potential modulation of
aromatase and sex steroid hormone receptors upon exposure
to tadalafil (TAD).
Methods Human osteoblast-like cells SAOS-2 were chosen
as an in vitro model system since osteoblasts are target
of steroid hormones. Cells were tested for viability upon
TAD exposure, which increased cell proliferation. Then,
cells were treated with/without TAD for several times to
evaluate potential modulation in PDE5, aromatase (ARO),
androgen (AR) and estrogen (ER) receptor expression.
Results Osteoblasts express significant levels of both PDE5
mRNA and protein. Exposure of cells to increasing concentrations
of TAD (10−8–10−7 M) decreased PDE5 mRNA and
protein expression. Also, TAD inhibited ARO mRNA and
protein expression leading to an increase in testosterone levels
in the supernatants. Interestingly, TAD increased total AR mRNA and protein expression and decreased ERα, with an
increased ratio of AR/ER, suggesting preferential androgenic
vs estrogenic pathway activation.
Conclusions Our results demonstrate for the first time
that TAD decreases ARO expression and increases AR
protein expression in human SAOS-2, strongly suggesting
a new control of steroid hormones pathway by PDE5i.
These findings might represent the first evidence of translational
actions of PDE5i on AR, which leads to hypothesize
a growing relevance of this molecule in men with
prostate cancer long-term treated with TAD for sexual
rehabilitation.
Keywords Tadalafil · Osteoblasts · Aromatase · Androgen
receptor · Estrogen recepto
The influence of doping with Ca and Mg in YBa2Cu3O7-δ ceramic
We have investigated the effect of partial substitution of Ca for Y and/or Mg for Cu on structural, compositional and magnetic properties in γBa 2 Cu 3 O 7-δ polycrystalline compounds. All prepared samples were found to be single phase with small fraction of Ba-secondary phases. Substitution by more than 2% of magnesium causes an increase of spurious phases. Energy Dispersive Spectroscopy (EDS) revealed that the distribution of Ca in the sample is quite homogenous. DC susceptibility measurements show that superconducting transition temperature Tc is reduced much more by Ca than Mg. Hysteresis loops reveal that magnetic irreversibility is decreased by Ca and Mg content. The deduced critical current density Jc does not follow the same variation. Ca alone reduces Jc for x=0.1 and x=0.2. Together with Ca, Mg compensates the reduction of Jc and increasing its content near the solubility limit gives higher Jc than in the undoped sample
Superconductivity in Sr2RuO4-Sr3Ru2O7 eutectic crystals
Superconducting behavior has been observed in the Sr2RuO4-Sr3Ru2O7 eutectic
system as grown by the flux-feeding floating zone technique. A supercurrent
flows across a single interface between Sr2RuO4 and Sr3Ru2O7 areas at distances
that are far beyond those expected in a conventional proximity scenario. The
current-voltage characteristics within the Sr3Ru2O7 macrodomain, as extracted
from the eutectic, exhibit signatures of superconductivity in the bilayered
ruthenate. Detailed microstructural, morphological and compositional analyses
address issues on the concentration and the size of Sr2RuO4 inclusions within
the Sr3Ru2O7 matrix. We speculate on the possibility of inhomogeneous
superconductivity in the eutectic Sr3Ru2O7 and exotic pairing induced by the
Sr2RuO4 inclusions.Comment: Pages 4, figures 3, submitted to Phys. Rev. Let
Tunnelling spectroscopy of the interface between Sr2RuO4 and a single Ru micro-inclusion in eutectic crystals
The understanding of the zero bias conductance peak (ZBCP) in the tunnelling
spectra of S/N junctions involving d-wave cuprate superconductors has been
important in the determination of the phase structure of the superconducting
order parameter. In this context, the involvement of a p-wave superconductor
such as Sr2RuO4 in tunnelling studies is indeed of great importance. We have
recently succeeded in fabricating devices that enable S/N junctions forming at
interfaces between Sr2RuO4 and Ru micro-inclusions in eutectic crystals to be
investigated.3 We have observed a ZBCP and have interpreted it as due to the
Andreev bound state, commonly seen in unconventional superconductors. Also we
have proposed that the onset of the ZBCP may be used to delineate the phase
boundary for the onset of a time reversal symmetry broken (TRSB) state within
the superconducting state, which does not always coincide with the onset of the
superconducting state. However, these measurements always involved two
interfaces between Sr2RuO4 and Ru. In the present study, we have extended the
previous measurements to obtain a deeper insight into the properties of a
single interface between Sr2RuO4 and Ru.Comment: To appear in J. Phys. Soc. Jpn. Vol. 75 No.12 issu
Superconducting properties of Nb thin films deposited on porous silicon templates
Porous silicon, obtained by electrochemical etching, has been used as a
substrate for the growth of nanoperforated Nb thin films. The films, deposited
by UHV magnetron sputtering on the porous Si substrates, inherited their
structure made of holes of 5 or 10 nm diameter and of 10 to 40 nm spacing,
which provide an artificial pinning structure. The superconducting properties
were investigated by transport measurements performed in the presence of
magnetic field for different film thickness and substrates with different
interpore spacing. Perpendicular upper critical fields measurements present
peculiar features such as a change in the H_c2(T) curvature and oscillations in
the field dependence of the superconducting resistive transition width at H=1
Tesla. This field value is much higher than typical matching fields in
perforated superconductors, as a consequence of the small interpore distance.Comment: accepted for publication on Journal of Applied Physic
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