3,530 research outputs found
Experimental manifestation of the breakpoint region in the current-voltage characteristics of intrinsic Josephson junctions
The experimental evidence of the breakpoint on the current-voltage
characteristics (IVCs) of the stacks of intrinsic Josephson junctions (IJJs) is
presented. The influence of the capacitive coupling on the IVCs of
BiSrCaCuO IJJs has been investigated. At 4.2 K, clear
breakpoint region is observed on the branches in the IVCs. It is found that the
hysteresis observed on the IVC is suppressed due to the coupling compared with
that expected from the McCumber parameter. Measurements agree well with the
results obtained by the theoretical model.Comment: 3 pages, 4 figure
Experimental observation of the longitudinal plasma excitation in intrinsic Josephson junctions
We have investigated the current-voltage characteristics (IVCs) of intrinsic
Josephson junctions (IJJs). Recently, it is predicted that the longitudinal
plasma wave can be excited by the parametric resonance in IJJs. Such an
excitation induces a singularity called as breakpoint region around switch back
region in the IVC. We have succeeded in the observation of the breakpoint
region in the IVC of the mesa with 5 IJJs at 4.2 K. Furthermore, it is found
that the temperature dependence of the breakpoint current is in agreement with
the theoretical prediction. This suggests that the wave number of the excited
plasma wave varies with temperature.Comment: 7 pages, 7 figures. Dubna-Nano2008, Accepted for JPCS
Symplectic capacity and short periodic billiard trajectory
We prove that a bounded domain in with smooth boundary has a
periodic billiard trajectory with at most bounce times and of length less
than , where is a positive constant which depends only on
, and is the supremum of radius of balls in . This
result improves the result by C.Viterbo, which asserts that has a
periodic billiard trajectory of length less than C'_n \vol(\Omega)^{1/n}. To
prove this result, we study symplectic capacity of Liouville domains, which is
defined via symplectic homology.Comment: 32 pages, final version with minor modifications. Published online in
Mathematische Zeitschrif
High Temperature Mixed State Axis Dissipation in Low Carrier Density
The nature of the out-of-plane dissipation was investigated in underdoped
single crystals at temperatures
close to the critical temperature. For this goal, temperature and angle
dependent out-of-plane resistivity measurements were carried out both below and
above the critical temperature. We found that the Ambegaokar-Halperin
relationship [V. Ambegaokar, and B. I. Halperin, Phys. Rev. Lett. \textbf{22},
1364 (1969)] depicts very well the angular magnetoresistivity in the
investigated range of field and temperature. The main finding is that the
in-plane phase fluctuations decouple the layers above the critical temperature
and the charge transport is governed only by the quasiparticles. We also have
calculated the interlayer Josephson critical current density, which was found
to be much smaller than the one predicted by the theory of layered
superconductors. This discrepancy could be a result of the d-wave symmetry of
the order parameter and/or of the non BCS temperature dependence of the c-axis
penetration length.Comment: Will appear in PR
Theory of BiSrCaCuO Cross-Whisker Josephson Junctions
Takano {\it et al.} [Phys. Rev. B {\bf 65}, 140513 (2002) and unpublished]
made Josephson junctions from single crystal whiskers of
BiSrCaCuO crossed an angle about the
axis.
From the mesa structures that formed at the cross-whisker interface, they
inferred a critical current density . Like the single crystal
results of Li {\it et al.} [Phys. Rev. Lett. {\bf 83}, 4160 (1999)], we show
that the whisker data are unlikely to result from a predominantly d-wave order
parameter. However, unlike the single crystals, these results, if correct,
require the whisker c-axis transport to be coherent.Comment: 5 pages, 4 figures, accepted for publication in Physical Review
Precision Measurements of d(d,p)t and d(d,n)^3He Total Cross Sections at Big-Bang Nucleosynthesis Energies
Recent Wilkinson Microwave Anisotropy Probe (WMAP) measurements have
determined the baryon density of the Universe with a precision of
about 4%. With tightly constrained, comparisons of Big Bang
Nucleosynthesis (BBN) abundance predictions to primordial abundance
observations can be made and used to test BBN models and/or to further
constrain abundances of isotopes with weak observational limits. To push the
limits and improve constraints on BBN models, uncertainties in key nuclear
reaction rates must be minimized. To this end, we made new precise measurements
of the d(d,p)t and d(d,n)^3He total cross sections at lab energies from 110 keV
to 650 keV.
A complete fit was performed in energy and angle to both angular distribution
and normalization data for both reactions simultaneously. By including
parameters for experimental variables in the fit, error correlations between
detectors, reactions, and reaction energies were accurately tabulated by
computational methods. With uncertainties around 2% +/- 1% scale error, these
new measurements significantly improve on the existing data set. At relevant
temperatures, using the data of the present work, both reaction rates are found
to be about 7% higher than those in the widely used Nuclear Astrophysics
Compilation of Reaction Rates (NACRE). These data will thus lead not only to
reduced uncertainties, but also to modifications in the BBN abundance
predictions.Comment: 15 pages, 11 figures, minor editorial change
Analytic Study for the String Theory Landscapes via Matrix Models
We demonstrate a first-principle analysis of the string theory landscapes in
the framework of non-critical string/matrix models. In particular, we discuss
non-perturbative instability, decay rate and the true vacuum of perturbative
string theories. As a simple example, we argue that the perturbative string
vacuum of pure gravity is stable; but that of Yang-Lee edge singularity is
inescapably a false vacuum. Surprisingly, most of perturbative minimal string
vacua are unstable, and their true vacuum mostly does not suffer from
non-perturbative ambiguity. Importantly, we observe that the instability of
these tachyon-less closed string theories is caused by ghost D-instantons (or
ghost ZZ-branes), the existence of which is determined only by non-perturbative
completion of string theory.Comment: v1: 5 pages, 2 figures; v2: references and footnote added; v3: 7
pages, 4 figures, organization changed, explanations expanded, references
added, reconstruction program from arbitrary spectral curves shown explicitl
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