1,379 research outputs found
The role of critical current on point contact Andreev Reflection spectrum between a normal metal and a superconductor
The point contact spectrum between a normal metal and a superconductor often
shows unexpected sharp dips in the conductance at voltage values larger than
the superconducting energy gap. These dips are not predicted in the
Blonder-Tinkham-Klapwizk (BTK) theory, commonly used to analyse these contacts.
We present here a systematic study of these dips in a variety of contacts
between different combinations of a superconductor and a normal metal. From the
correlation between the characteristics of these dips with the contact area, we
can surmise that such dips are caused by the contact not being in the ballistic
limit. An analysis of the possible errors introduced while analysing such a
spectrum with the standard BTK model is also presented.Comment: 16 pages, PS, figure include
Remarks on flavour mixings from orbifold compactification
We consider 5d SU(5) GUT models based on the orbifold , and study the different possibilities of placing the SU(5) matter
multiplets in three possible locations, namely, the two branes at the two
orbifold fixed points and SU(5) bulk. We demonstrate that if flavour
hierarchies originate solely from geometrical suppressions due to wavefunction
normalisation of fields propagating in the bulk, then it is not possible to
satisfy even the gross qualitative behaviour of the CKM and MNS matrices
regardless of where we place the matter multiplets.Comment: 4 pages, Late
Constraining the charged Higgs mass in the left-right symmetric model from b --> s
In the context of the left--right symmetric model, the decay b \rightarrow s \gamma receives contributions from the gauge interactions mediated mainly by the W_L, through W_L--W_R mixing and also from the Yukawa interactions of the charged and the neutral (flavour-changing) scalars (the latter type of Yukawa interaction has been overlooked in the previous literature). Following the recent CLEO measurement of the inclusive b \rightarrow s \gamma process and the measurement of the top-quark mass by the CDF and D0 collaborations, the parameter space of the left--right symmetric model are more squeezed than before
A 'p-n' diode with hole and electron-doped lanthanum manganite
The hole-doped manganite La0.7Ca0.3MnO3 and the electron-doped manganite
La0.7Ce0.3MnO3 undergo an insulator to metal transition at around 250 K, above
which both behave as a polaronic semiconductor. We have successfully fabricated
an epitaxial trilayer (La0.7Ca0.3MnO3/SrTiO3/La0.7Ce0.3MnO3), where SrTiO3 is
an insulator. At room temperature, i.e. in the semiconducting regime, it
exhibits asymmetric current-voltage (I-V) characteristics akin to a p-n diode.
The observed asymmetry in the I-V characteristics disappears at low
temperatures where both the manganite layers are metallic. To the best of our
knowledge, this is the first report of such a p-n diode, using the polaronic
semiconducting regime of doped manganites.Comment: PostScript text and 2 figures, to be published in Appl. Phys. Lett
Possible observation of coulomb blockade at room temperature
We have studied the (I-V) characteristics of the tunnel junction formed between the tip and the substrate in an STM at room temperature. We find that in such an arrangement it may be possible to get a junction capacitance ⋍10−19 F and junction conductance < 1 μs. When the junction conductance is < 1 μs strong nonlinearity is observed in the (I-V) characteristics. We explain this nonlinearity as onset of coulomb blockade of tunneling electrons
Self-gravitating spheres of anisotropic fluid in geodesic flow
The fluid models mentioned in the title are classified. All characteristics
of the fluid are expressed through a master potential, satisfying an ordinary
second order differential equation. Different constraints are imposed on this
core of relations, finding new solutions and deriving the classical results for
perfect fluids and dust as particular cases. Many uncharged and charged
anisotropic solutions, all conformally flat and some uniform density solutions
are found. A number of solutions with linear equation among the two pressures
are derived, including the case of vanishing tangential pressure.Comment: 21 page
Universal scaling of the order-parameter distribution in strongly disordered superconductors
We investigate theoretically and experimentally the statistical properties of
the inhomogeneous order-parameter distribution (OPD) at the verge of the
superconductor-insulator transition (SIT). We find within two prototype
fermionic and bosonic models for disordered superconductors that one can
identify a universal rescaling of the OPD. By performing scanning-tunneling
microscopy experiments in three samples of NbN with increasing disorder we show
that such a rescaling describes also with an excellent accuracy the
experimental data. These results can provide a breakthrough in our
understanding of the SIT.Comment: 11 pages, 8 figures, revised version submitted to PR
Relativistic X-ray reflection and highly ionized absorption in the spectrum of NS LMXB 1A 1744-361
We present the results from the spectral and timing analysis of the accreting
neutron star 1A~1744-361 from the \nustar{} observation performed in its 2022
outbursts. The unabsorbed bolometric X-ray luminosity during this observation
in the energy band 0.1-100\kev{} is erg~s,
assuming a distance of kpc. During this observation, the source was in the
banana branch of the atoll track. The source spectrum exhibits relativistic
disc reflection and clear absorption features when an absorbed blackbody and
cut-off power-law model describes the continuum emission. The 3-50\kev{}
source spectrum is well fitted using a model combination consisting of an
absorbed single-temperature blackbody and a reflection model along with the
addition of a warm absorber component. The inner-disk radius, ,
obtained from the reflection fit is
( km for a 1.4\Msun NS). This measurement allowed us to further
constrain the magnetic field strength to G. The
strong absorption features \sim 6.91\kev{} and \sim 7.99\kev{} imply the
presence of highly ionized absorbing material with a column density of
cm, emanating from the accretion disk in the form
of disc wind with an outflow velocity of km
s.Comment: 10 pages, 10 figures, Submitted to MNRAS main journa
Development of New-Concept Clean Technologies to Extract Metals from Primary and Secondary Sources
Development of new-concept hydrometallurical technologies promoted by Tecnicas Reunidas is providing efficient and clean means for metals extraction from diverse primary & secondary sources, such as conventional or low-grade concentrates and ores, lead-acid batteries, domestic batteries, effluents from electronic industry, etc. Rele-vant characteristics of the recently developed processes regarding extraction of zinc, lead, silver, nickel and copper metals are the following: environmentally friendly, value added products and by-products, flexibility to a great variety of feed materials, adapted to local market requirements, easy to be combined with existing plants available for small and large capacities and on-site installation close to the metal sources
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