529 research outputs found
Semi-relativistic description of quasielastic neutrino reactions and superscaling in a continuum shell model
The so-called semi-relativistic expansion of the weak charged current in
powers of the initial nucleon momentum is performed to describe
charge-changing, quasielastic neutrino reactions at
intermediate energies. The quality of the expansion is tested by comparing with
the relativistic Fermi gas model using several choices of kinematics of
interest for ongoing neutrino oscillation experiments. The new current is then
implemented in a continuum shell model together with relativistic kinematics to
investigate the scaling properties of and cross
sections.Comment: 33 pages, 10 figures, to appear in PR
Interaction of intense vuv radiation with large xenon clusters
The interaction of atomic clusters with short, intense pulses of laser light
to form extremely hot, dense plasmas has attracted extensive experimental and
theoretical interest. The high density of atoms within the cluster greatly
enhances the atom--laser interaction, while the finite size of the cluster
prevents energy from escaping the interaction region. Recent technological
advances have allowed experiments to probe the laser--cluster interaction at
very high photon energies, with interactions much stronger than suggested by
theories for lower photon energies. We present a model of the laser--cluster
interaction which uses non-perturbative R-matrix techniques to calculate
inverse bremsstrahlung and photoionization cross sections for Herman-Skillman
atomic potentials. We describe the evolution of the cluster under the influence
of the processes of inverse bremsstrahlung heating, photoionization,
collisional ionization and recombination, and expansion of the cluster. We
compare charge state distribution, charge state ejection energies, and total
energy absorbed with the Hamburg experiment of Wabnitz {\em et al.} [Nature
{\bf 420}, 482 (2002)] and ejected electron spectra with Laarmann {\em et al.}
[Phys. Rev. Lett. {\bf 95}, 063402 (2005)]
Effective range function below threshold
We demonstrate that the kernel of the Lippmann-Schwinger equation, associated
with interactions consisting of a sum of the Coulomb plus a short range nuclear
potential, below threshold becomes degenerate. Taking advantage of this fact,
we present a simple method of calculating the effective range function for
negative energies. This may be useful in practice since the effective range
expansion extrapolated to threshold allows to extract low-energy scattering
parameters: the Coulomb-modified scattering length and the effective range.Comment: 14 pages, 1 figur
Three-potential formalism for the three-body scattering problem with attractive Coulomb interactions
A three-body scattering process in the presence of Coulomb interaction can be
decomposed formally into a two-body single channel, a two-body multichannel and
a genuine three-body scattering. The corresponding integral equations are
coupled Lippmann-Schwinger and Faddeev-Merkuriev integral equations. We solve
them by applying the Coulomb-Sturmian separable expansion method. We present
elastic scattering and reaction cross sections of the system both below
and above the threshold. We found excellent agreements with previous
calculations in most cases.Comment: 12 pages, 3 figure
Continued fraction representation of the Coulomb Green's operator and unified description of bound, resonant and scattering states
If a quantum mechanical Hamiltonian has an infinite symmetric tridiagonal
(Jacobi) matrix form in some discrete Hilbert-space basis representation, then
its Green's operator can be constructed in terms of a continued fraction. As an
illustrative example we discuss the Coulomb Green's operator in
Coulomb-Sturmian basis representation. Based on this representation, a quantum
mechanical approximation method for solving Lippmann-Schwinger integral
equations can be established, which is equally applicable for bound-, resonant-
and scattering-state problems with free and Coulombic asymptotics as well. The
performance of this technique is illustrated with a detailed investigation of a
nuclear potential describing the interaction of two particles.Comment: 7 pages, 4 ps figures, revised versio
Fermi surface and quasiparticle dynamics of Na(x)CoO2 {x=0.7} investigated by Angle-Resolved Photoemission Spectroscopy
We present an angle-resolved photoemission study of Na0.7CoO2, the host
cobaltate of the NaxCoO2.yH2O series. Our results show a large hexagonal-like
hole-type Fermi surface, an extremely narrow strongly renormalized
quasiparticle band and a small Fermi velocity. Along the Gamma to M high
symmetry line, the quasiparticle band crosses the Fermi level from M toward
Gamma consistent with a negative sign of effective single-particle hopping (t
): t is estimated to be about 8 meV which is on the order of exchange coupling
J in this system. This suggests that t ~ J ~ 10 meV is an important energy
scale in the system. Quasiparticles are well defined only in the T-linear
resistivity regime. Small single particle hopping and unconventional
quasiparticle dynamics may have implications for understanding the unusual
behavior of this new class of compounds.Comment: Revised text, Added Figs, Submitted to PR
Spin polarization of the L-gap surface states on Au(111)
The electron spin polarization (ESP) of the L-gap surface states on Au(111)
is investigated theoretically by means of first-principles electronic-structure
and photoemission calculations. The surface states show a large spin-orbit
induced in-plane ESP which is perpendicular to the in-plane wavevector, in
close analogy to a two-dimensional electron gas with Rashba spin-orbit
interaction. The surface corrugation leads to a small ESP component normal to
the surface, being not reported so far. The surface-states ESP can be probed
qualitatively and quantitatively by spin- and angle-resolved photoelectron
spectroscopy, provided that the initial-state ESP is retained in the
photoemission process and not obscured by spin-orbit induced polarization
effects. Relativistic photoemission calculations provide detailed information
on what photoemission set-ups allow to conclude from the photoelectron ESP on
that of the surface states.Comment: 22 pages with 8 figure
Origins of large critical temperature variations in single layer cuprates
We study the electronic structures of two single layer superconducting
cuprates, TlBaCuO (Tl2201) and
(BiPb)(SrLa)CuO (Bi2201) which
have very different maximum critical temperatures (90K and 35K respectively)
using Angular Resolved Photoemission Spectroscopy (ARPES). We are able to
identify two main differences in their electronic properties. First, the shadow
band that is present in double layer and low T single layer cuprates
is absent in Tl2201. Recent studies have linked the shadow band to structural
distortions in the lattice and the absence of these in Tl2201 may be a
contributing factor in its T.Second, Tl2201's Fermi surface (FS)
contains long straight parallel regions near the anti-node, while in Bi2201 the
anti-nodal region is much more rounded. Since the size of the superconducting
gap is largest in the anti-nodal region, differences in the band dispersion at
the anti-node may play a significant role in the pairing and therefore affect
the maximum transition temperature.Comment: 6 pages, 5 figures,1 tabl
Doping dependence of the shadow band in La-based cuprates studied by angle-resolved photoemission spectroscopy
The shadow band (SB) in La-based cuprate family (La214) was
studied by angle-resolved photoemission spectroscopy (ARPES) over a wide doping
range from to . Unlike the well-studied case of the Bi-based
cuprate family, an overall strong, monotonic doping dependence of the SB
intensity at the Fermi level () was observed. In contrast to a previous
report for the presence of the SB only close to , we found it exists in
a wide doping range, associated with a doping-independent wave
vector but strongly doping-dependent intensity: It is the strongest at and systematically diminishes as the doping increases until it becomes
negligible in the overdoped regime. This SB with the observed doping dependence
of intensity can in principle be caused by the antiferromagnetic fluctuations
or a particular form of low-temperature orthorhombic lattice distortion known
to persist up to in the system, with both being weakened with
increasing doping. However, a detailed binding energy dependent analysis of the
SB at does not appear to support the former interpretation, leaving
the latter as a more plausible candidate, despite a challenge in quantitatively
linking the doping dependences of the SB intensity and the magnitude of the
lattice distortion. Our finding highlights the necessity of a careful and
global consideration of the inherent structural complications for correctly
understanding the cuprate Fermiology and its microscopic implication.Comment: Note the revised conclusion and author list; To appear in New J. Phy
The Asakura-Oosawa model in the protein limit: the role of many-body interactions
We study the Asakura-Oosawa model in the "protein limit", where the
penetrable sphere radius is much greater than the hard sphere radius
. The phase behaviour and structure calculated with a full many-body
treatment show important qualitative differences when compared to a description
based on pair potentials alone. The overall effect of the many-body
interactions is repulsive.Comment: 9 pages and 11 figures, submitted to J. Phys.: Condensed Matter,
special issue "Effective many-body interactions and correlations in soft
matter
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