9,482 research outputs found
Electronic Structure of Lanthanum Hydrides with Switchable Optical Properties
Recent dramatic changes in the optical properties of LaH_{2+x} and YH_{2+x}
films discovered by Huiberts et al. suggest their electronic structure is
described best by a local model. Electron correlation is important in H^-
-centers and in explaining the transparent insulating behavior of LaH_3. The
metal-insulator transition at takes place in a band of highly
localized states centered on the -vacancies in the LaH_3 structure.Comment: plain tex, 3 figure
Spintronic transport and Kondo effect in quantum dots
We investigate the spin-dependent transport properties of quantum-dot based
structures where Kondo correlations dominate the electronic dynamics. The
coupling to ferromagnetic leads with parallel magnetizations is known to give
rise to nontrivial effects in the local density of states of a single quantum
dot. We show that this influence strongly depends on whether charge
fluctuations are present or absent in the dot. This result is confirmed with
numerical renormalization group calculations and perturbation theory in the
on-site interaction. In the Fermi-liquid fixed point, we determine the
correlations of the electric current at zero temperature (shot noise) and
demonstrate that the Fano factor is suppressed below the Poissonian limit for
the symmetric point of the Anderson Hamiltonian even for nonzero lead
magnetizations. We discuss possible avenues of future research in this field:
coupling to the low energy excitations of the ferromagnets (magnons), extension
to double quantum dot systems with interdot antiferromagnetic interaction and
effect of spin-polarized currents on higher symmetry Kondo states such as
SU(4).Comment: 11 pages, 5 figures. Proceedings of the 3rd Intl. Conf. on Physics
and Applications of Spin-Related Phenomena in Semiconductors, Santa Barbara,
200
Self-organized Emergence of Navigability on Small-World Networks
This paper mainly investigates why small-world networks are navigable and how
to navigate small-world networks. We find that the navigability can naturally
emerge from self-organization in the absence of prior knowledge about
underlying reference frames of networks. Through a process of information
exchange and accumulation on networks, a hidden metric space for navigation on
networks is constructed. Navigation based on distances between vertices in the
hidden metric space can efficiently deliver messages on small-world networks,
in which long range connections play an important role. Numerical simulations
further suggest that high cluster coefficient and low diameter are both
necessary for navigability. These interesting results provide profound insights
into scalable routing on the Internet due to its distributed and localized
requirements.Comment: 3 figure
First Observation of Radiative B^0 -> \phi K^0 \gamma Decays and Measurements of Their Time-Dependent CP Violation
We report the first observation of the radiative decay B^0 -> \phi K^0 \gamma
using a data sample of 772 x 10^6 B B-bar pairs collected at the \Upsilon(4S)
resonance with the Belle detector at the KEKB asymmetric-energy e^+e^-
collider. We observe a signal of 37+/-8 events with a significance of 5.4
standard deviations including systematic uncertainties. The measured branching
fraction is , where the uncertainties are statistical and systematic, respectively.
We also report the first measurements of time-dependent CP violation
parameters: and . Furthermore, we measure , and find that the signal is concentrated in
the M_{\phi K} mass region near threshold.Comment: 6 pages, 3 figures, Modified version is to be published in PRD(RC
Search for decays to invisible final states at Belle
We report a search for decays into invisible final states using a
data sample of pairs collected at the
resonance with the Belle detector at the KEKB
collider. The signal is identified by fully reconstructing a hadronic decay of
the accompanying meson and requiring no other particles in the event. No
significant signal is observed, and we obtain an upper limit of at the 90% confidence level for the branching fraction of invisible
decay.Comment: 6 pages, 5 figures (9 figure files
Exact ground states for the four-electron problem in a two-dimensional finite Hubbard square system
We present exact explicit analytical results describing the exact ground
state of four electrons in a two dimensional square Hubbard cluster containing
16 sites taken with periodic boundary conditions. The presented procedure,
which works for arbitrary even particle number and lattice sites, is based on
explicitly given symmetry adapted base vectors constructed in r-space. The
Hamiltonian acting on these states generates a closed system of 85 linear
equations providing by its minimum eigenvalue the exact ground state of the
system. The presented results, described with the aim to generate further
creative developments, not only show how the ground state can be exactly
obtained and what kind of contributions enter in its construction, but
emphasize further characteristics of the spectrum. On this line i) possible
explications are found regarding why weak coupling expansions often provide a
good approximation for the Hubbard model at intermediate couplings, or ii)
explicitly given low lying energy states of the kinetic energy, avoiding double
occupancy, suggest new roots for pairing mechanism attracting decrease in the
kinetic energy, as emphasized by kinetic energy driven superconductivity
theories.Comment: 37 pages, 18 figure
Search for CP Violation in the Decay
We search for CP violation in the decay using a
data sample with an integrated luminosity of 977 fb collected with the
Belle detector at the KEKB asymmetric-energy collider. No CP violation
has been observed and the CP asymmetry in decay is
measured to be , which is the most sensitive
measurement to date. After subtracting CP violation due to
mixing, the CP asymmetry in decay is found to be
.Comment: 15 pages, 4 figures, 1 table. Published in JHE
Observation of and search for in B decays
We report a study of and
decay modes using events collected at the
\Upsilon(4S)e^+ e^-X(3872) \to J/\psi \gamma\chi_{c2} \to J/\psi \gammaB\to (X_{c\bar{c}}\gamma) KX(3872) \to \psi' \gamma\mathcal{B}(B^{\pm} \to X(3872)
K^{\pm}) \mathcal{B}(X(3872) \to J/\psi\gamma)=(1.78^{+0.48}_{-0.44}\pm
0.12)\times 10^{-6}\mathcal{B} (B^{\pm} \to\chi_{c2} K^{\pm})=(1.11^{+0.36}_{-0.34} \pm 0.09) \times 10^{-5}\mathcal{B}(B^{\pm} \to
X(3872) K^{\pm}) \mathcal{B}(X(3872) \to \psi'\gamma)<3.45\times 10^{-6}$
(upper limit at 90% C.L.) and also provide upper limits for other searches.Comment: 6 pages, 3 figure
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