1,630 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
GUTs with dim-5 interactions: Gauge Unification and Intermediate Scales
Dimension-5 corrections to the gauge kinetic term of Grand Unified Theories
(GUTs) may capture effects of quantum gravity or string compactification. Such
operators modify the usual gauge coupling unification prediction in a
calculable manner. Here we examine SU(5), SO(10), and E(6) GUTs in the light of
all such permitted operators and calculate the impact on the intermediate
scales and the unification programme. We show that in many cases at least one
intermediate scale can be lowered to even 1-10 TeV, where a neutral Z' and
possibly other states are expected.Comment: 23 pages, 8 figures, 10 tables, Treatment of U(1) mixing effects
corrected. Published version
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
Boosted Top Quark Signals for Heavy Vector Boson Excitations in a Universal Extra Dimension Model
In view of the fact that the Kaluza-Klein (KK) modes in a model with
a Universal Extra Dimension (UED), could mimic supersymmetry signatures at the
LHC, it is necessary to look for the KK modes, which have no analogues
in supersymmetry. We discuss the possibility of searching for heavy
vector boson resonances -- especially the -- through their decays to a
highly-boosted top quark-antiquark pair using recently-developed top-jet
tagging techniques in the hadronic channel. It is shown that signals
from the gluon resonance are as efficient a discovery mode at the LHC
as dilepton channels from the and resonances.Comment: 22 pages, 8 embedded figure
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
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