1,587 research outputs found
Resonant-state expansion of the Green's function of open quantum systems
Our series of recent work on the transmission coefficient of open quantum
systems in one dimension will be reviewed. The transmission coefficient is
equivalent to the conductance of a quantum dot connected to leads of quantum
wires. We will show that the transmission coefficient is given by a sum over
all discrete eigenstates without a background integral. An apparent
"background" is in fact not a background but generated by tails of various
resonance peaks. By using the expression, we will show that the Fano asymmetry
of a resonance peak is caused by the interference between various discrete
eigenstates. In particular, an unstable resonance can strongly skew the peak of
a nearby resonance.Comment: 7 pages, 7 figures. Submitted to International Journal of Theoretical
Physics as an article in the Proceedings for PHHQP 2010
(http://www.math.zju.edu.cn/wjd/
A Cross-Whiskers Junction as a Novel Fabrication Process for Intrinsic Josephson Junction
A Bi2Sr2CaCu2O8+d cross-whiskers junction has been successfully discovered as
a novel intrinsic Josephson junction without using any technique for
micro-fabrication. Two Bi2Sr2CaCu2O8+d whisker crystals were placed crosswise
on a MgO substrate and heated at 850C for 30 min. They were electrically
connected at their c-planes. The measurement terminals were made at the four
ends of the whiskers. The I-V characteristics of the cross-whiskers junction at
5K were found to show a clear multiple-branch structure with a spacing of
approximately 15 mV that is a feature of the intrinsic Josephson junction. The
critical current density Jc was estimated to be 1170 A/cm2. The
branch-structure was strongly suppressed by the magnetic field above 1kOe.Comment: 4 pages, PDF fil
Non-Hermitian Delocalization and Eigenfunctions
Recent literature on delocalization in non-Hermitian systems has stressed
criteria based on sensitivity of eigenvalues to boundary conditions and the
existence of a non-zero current. We emphasize here that delocalization also
shows up clearly in eigenfunctions, provided one studies the product of left-
and right-eigenfunctions, as required on physical grounds, and not simply the
squared modulii of the eigenfunctions themselves. We also discuss the right-
and left-eigenfunctions of the ground state in the delocalized regime and
suggest that the behavior of these functions, when considered separately, may
be viewed as ``intermediate'' between localized and delocalized.Comment: 8 pages, 11 figures include
Superconductivity in CVD Diamond Thin Film Well-Above Liquid Helium Temperature
Diamond has always been adored as a jewel. Even more fascinating is its
outstanding physical properties; it is the hardest material known in the world
with the highest thermal conductivity. Meanwhile, when we turn to its
electrical properties, diamond is a rather featureless electrical insulator.
However, with boron doping, it becomes a p-type semiconductor, with boron
acting as a charge acceptor. Therefore the recent news of superconductivity in
heavily boron-doped diamond synthesized by high pressure sintering was received
with considerable surprise. Opening up new possibilities for diamond-based
electrical devices, a systematic investigation of these phenomena clearly needs
to be achieved. Here we show unambiguous evidence of superconductivity in a
diamond thin film deposited by a chemical vapor deposition (CVD) method.
Furthermore the onset of the superconducting transition is found to be 7.4K,
which is higher than the reported value in ref(7) and well above helium liquid
temperature. This finding establishes the superconductivity to be a universal
property of boron-doped diamond, demonstrating that device application is
indeed a feasible challenge.Comment: 6 pages, 3 figure
Finite Size Effects in Vortex Localization
The equilibrium properties of flux lines pinned by columnar disorder are
studied, using the analogy with the time evolution of a diffusing scalar
density in a randomly amplifying medium. Near H_{c1}, the physical features of
the vortices in the localized phase are shown to be determined by the density
of states near the band edge. As a result, H_{c1} is inversely proportional to
the logarithm of the sample size, and the screening length of the perpendicular
magnetic field decreases with temperature. For large tilt the extended ground
state turns out to wander in the plane perpendicular to the defects with
exponents corresponding to a directed polymer in a random medium, and the
energy difference between two competing metastable states in this case is
extensive. The divergence of the effective potential associated with strong
pinning centers as the tilt approaches its critical value is discussed as well.Comment: 10 pages, 2 figure
d-like Symmetry of the Order Parameter and Intrinsic Josephson Effects in Bi2212 Cross-Whisker Junctions
An intrinsic tunnel junction was made using two Bi-2212 single crystal
whiskers. The two whiskers with a cross-angle were overlaid at their c-planes
and connected by annealing. The angular dependence of the critical current
density along the c-axis is of the d-wave symmetry. However, the angular
dependence is much stronger than that of the conventional d-wave. Furthermore,
the current vs. voltage characteristics of the cross-whiskers junctions show a
multiple-branch structure at any cross-angle, indicating the formation of the
intrinsic Josephson junction array.Comment: 4 pages PDF fil
Winding Numbers, Complex Currents, and Non-Hermitian Localization
The nature of extended states in disordered tight binding models with a
constant imaginary vector potential is explored. Such models, relevant to
vortex physics in superconductors and to population biology, exhibit a
delocalization transition and a band of extended states even for a one
dimensional ring. Using an analysis of eigenvalue trajectories in the complex
plane, we demonstrate that each delocalized state is characterized by an
(integer) winding number, and evaluate the associated complex current. Winding
numbers in higher dimensions are also discussed.Comment: 4 pages, 2 figure
Global universality of the two-layer neural network with the -rectified linear unit
This paper concerns the universality of the two-layer neural network with the
-rectified linear unit activation function with with a
suitable norm without any restriction on the shape of the domain. This type of
result is called global universality, which extends the previous result for
by the present authors. This paper covers -sigmoidal functions as an
application of the fundamental result on -rectified linear unit functions
Spectrum Analysis of the Type Ib Supernova 1999dn: Probable Identifications of C II and H-alpha
Low resolution spectra of SN 1999dn at early times are presented and compared
with synthetic spectra generated with the parameterized supernova
synthetic-spectrum code SYNOW. We find that the spectra of SN 1999dn strongly
resemble those of SN 1997X and SN 1984L, and hence we classify it as a Type Ib
event. Line-identifications are established through spectrum synthesis. Strong
evidence of both H-alpha and C II 6580 is found. We infer that H-alpha appears
first, before the time of maximum brightness, and then is blended with and
finally overwhelmed by the C II line after maximum; this favors a thin
high-velocity hydrogen skin in this Type Ib supernova.Comment: 15 pages, 3 figures. Accepted for publication in Ap
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