2,025 research outputs found
Surface-induced magnetic anisotropy for impurity spins in granular AuFe films
The theory of the surface-induced anisotropy is extended to the case of
granular films of dilute magnetic alloys. Since the surface-induced blocking of
a magnetic-impurity spin appears to be very sensitive to the specific
polycrystalline structure, we speculate that the apparent discrepancy between
the experimental results of different groups for the size dependence of the
Kondo resistivity can be linked to different microstructure of the samples. We
apply our model to calculate the magnetization of impurity spins in small AuFe
grains and to interpret the experimental data on the anomalous Hall effect in
thin Fe doped Au films.Comment: 4 pages, 5 figures, E-mail addresses: [email protected],
[email protected], [email protected]
Self-trapping transition for nonlinear impurities embedded in a Cayley tree
The self-trapping transition due to a single and a dimer nonlinear impurity
embedded in a Cayley tree is studied. In particular, the effect of a perfectly
nonlinear Cayley tree is considered. A sharp self-trapping transition is
observed in each case. It is also observed that the transition is much sharper
compared to the case of one-dimensional lattices. For each system, the critical
values of for the self-trapping transitions are found to obey a
power-law behavior as a function of the connectivity of the Cayley tree.Comment: 6 pages, 7 fig
Impact of Subleading Corrections on Hadronic B Decays
We study the subleading corrections originating from the 3-parton (q\bar q g)
Fock states of final-state mesons in B decays. The corrections could give
significant contributions to decays involving an \omega or \eta^{(\prime)} in
the final states. Our results indicate the similarity of \omega K and \omega
\pi^- rates, of order 5\times 10^{-6}, consistent with the recent measurements.
We obtain a_2(B\to J/\psi K)\approx 0.27+0.05i, in good agreement with data.
Without resorting to the unknown singlet annihilation effects, 3-parton Fock
state contributions can enhance the branching ratios of K\eta' to the level
above 50\times 10^{-6}.Comment: 5 pages, 5 figures, revtex4; some typos corrected, a new figure and a
reference added, more explanations for the calculation provided, to appear in
Phys. Rev.
Intrinsic tunneling spectroscopy: A look from the inside at HTSC
Layered structure of Bi-2212 high superconductor (HTSC), provides a
unique opportunity to probe quasiparticle density of states inside a bulk
single crystal by means of intrinsic (interlayer) tunneling spectroscopy. Here
I present a systematic study of intrinsic tunneling characteristics of Bi-2212
as a function of doping, temperature, magnetic field and intercalation. An
improved resolution made it possible to simultaneously trace the
superconducting gap (SG) and the normal state pseudo-gap (PG) in a close
vicinity of and to analyze closing of the PG at . The obtained
doping phase diagram exhibits a critical doping point for appearance of the PG
and a characteristic crossing of the SG and the PG close to the optimal doping.
All this points towards coexistence of two different and competing order
parameters in Bi-2212.Comment: 4 pages, 5 figures, Presentation at M2S-Rio (May 2003), Subm. to
Physica C. Note: A discussion of magnetic field dependencies is adde
Phase of the Wilson Line at High Temperature in the Standard Model
We compute the effective potential for the phase of the Wilson line at high
temperature in the standard model to one loop order. Besides the trivial vacua,
there are metastable states in the direction of hypercharge. Assuming
that the universe starts out in such a metastable state at the Planck scale, it
easily persists to the time of the electroweak phase transition, which then
proceeds by an unusual mechanism. All remnants of the metastable state
evaporate about the time of the phase transition.Comment: 4 pages in ReVTeX plus 1 figure; Columbia Univ. preprint CU-TP-63
Semiclassical Quantization for the Spherically Symmetric Systems under an Aharonov-Bohm magnetic flux
The semiclassical quantization rule is derived for a system with a
spherically symmetric potential and an
Aharonov-Bohm magnetic flux. Numerical results are presented and compared with
known results for models with . It is shown that the
results provided by our method are in good agreement with previous results. One
expects that the semiclassical quantization rule shown in this paper will
provide a good approximation for all principle quantum number even the rule is
derived in the large principal quantum number limit . We also discuss
the power parameter dependence of the energy spectra pattern in this
paper.Comment: 13 pages, 4 figures, some typos correcte
New exact solution of Dirac-Coulomb equation with exact boundary condition
It usually writes the boundary condition of the wave equation in the Coulomb
field as a rough form without considering the size of the atomic nucleus. The
rough expression brings on that the solutions of the Klein-Gordon equation and
the Dirac equation with the Coulomb potential are divergent at the origin of
the coordinates, also the virtual energies, when the nuclear charges number Z >
137, meaning the original solutions do not satisfy the conditions for
determining solution. Any divergences of the wave functions also imply that the
probability density of the meson or the electron would rapidly increase when
they are closing to the atomic nucleus. What it predicts is not a truth that
the atom in ground state would rapidly collapse to the neutron-like. We
consider that the atomic nucleus has definite radius and write the exact
boundary condition for the hydrogen and hydrogen-like atom, then newly solve
the radial Dirac-Coulomb equation and obtain a new exact solution without any
mathematical and physical difficulties. Unexpectedly, the K value constructed
by Dirac is naturally written in the barrier width or the equivalent radius of
the atomic nucleus in solving the Dirac equation with the exact boundary
condition, and it is independent of the quantum energy. Without any divergent
wave function and the virtual energies, we obtain a new formula of the energy
levels that is different from the Dirac formula of the energy levels in the
Coulomb field.Comment: 12 pages,no figure
Sharp increase of the effective mass near the critical density in a metallic 2D electron system
We find that at intermediate temperatures, the metallic temperature
dependence of the conductivity \sigma(T) of 2D electrons in silicon is
described well by a recent interaction-based theory of Zala et al. (Phys. Rev.
B 64, 214204 (2001)). The tendency of the slope d\sigma/dT to diverge near the
critical electron density is in agreement with the previously suggested
ferromagnetic instability in this electron system. Unexpectedly, it is found to
originate from the sharp enhancement of the effective mass, while the effective
Lande g factor remains nearly constant and close to its value in bulk silicon
Rare Decays of \Lambda_b->\Lambda + \gamma and \Lambda_b ->\Lambda + l^{+} l^{-} in the Light-cone Sum Rules
Within the Standard Model, we investigate the weak decays of and with the light-cone
sum rules approach. The higher twist distribution amplitudes of
baryon to the leading conformal spin are included in the sum rules for
transition form factors. Our results indicate that the higher twist
distribution amplitudes almost have no influences on the transition form
factors retaining the heavy quark spin symmetry, while such corrections can
result in significant impacts on the form factors breaking the heavy quark spin
symmetry. Two phenomenological models (COZ and FZOZ) for the wave function of
baryon are also employed in the sum rules for a comparison, which can
give rise to the form factors approximately 5 times larger than that in terms
of conformal expansion. Utilizing the form factors calculated in LCSR, we then
perform a careful study on the decay rate, polarization asymmetry and
forward-backward asymmetry, with respect to the decays of , .Comment: 38 pages, 15 figures, some typos are corrected and more references
are adde
Resonant nature of phonon-induced damping of Rabi oscillations in quantum dots
Optically controlled coherent dynamics of charge (excitonic) degrees of
freedom in a semiconductor quantum dot under the influence of lattice dynamics
(phonons) is discussed theoretically. We show that the dynamics of the lattice
response in the strongly non-linear regime is governed by a semiclassical
resonance between the phonon modes and the optically driven dynamics. We stress
on the importance of the stability of intermediate states for the truly
coherent control.Comment: 4 pages, 2 figures; final version; moderate changes, new titl
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