2,839 research outputs found
Nuclear electromagnetic dipole response with the Self-Consistent Green's Function formalism
Microscopic calculations of the electromagnetic response of medium-mass
nuclei are now feasible thanks to the availability of realistic nuclear
interactions with accurate saturation and spectroscopic properties, and the
development of large-scale computing methods for many-body physics. The purpose
is to compute isovector dipole electromagnetic (E1) response and related
quantities, i.e. integrated dipole cross section and polarizability, and
compare with data from photoabsorption and Coulomb excitation experiments. The
single-particle propagator is obtained by solving the Dyson equation, where the
self-energy includes correlations non-perturbatively through the Algebraic
Diagrammatic Construction (ADC) method. The particle-hole () polarization
propagator is treated in the Dressed Random Phase Approximation (DRPA), based
on an effective correlated propagator that includes some effects but
keeps the same computation scaling as the standard Hartree-Fock propagator. The
E1 responses for O, Ca and Ni have
been computed: the presence of a soft dipole mode of excitation for
neutron-rich nuclei is found, and there is a fair reproduction of the
low-energy part of the experimental excitation spectrum. This is reflected in a
good agreement with the empirical dipole polarizability values. For a realistic
interaction with an accurate reproduction of masses and radii up to medium-mass
nuclei, the Self-Consistent Green's Function method provides a good description
of the E1 response, especially in the part of the excitation spectrum below the
Giant Dipole Resonance. The dipole polarizability is largely independent from
the strategy of mapping the dressed propagator to a simplified one that is
computationally manageableComment: 14 pages, 12 figure
Onsager relations in a two-dimensional electron gas with spin-orbit coupling
Theory predicts for the two-dimensional electrons gas with only Rashba
spin-orbit interaction a vanishing spin Hall conductivity and at the same time
a finite inverse spin Hall effect. We show how these seemingly contradictory
results are compatible with the Onsager relations: the latter do hold for spin
and particle (charge) currents in the two-dimensional electron gas, although
(i) their form depends on the experimental setup and (ii) a vanishing bulk spin
Hall conductivity does not necessarily imply a vanishing spin Hall effect. We
also discuss the situation in which extrinsic spin orbit from impurities is
present and the bulk spin Hall conductivity can be different from zero.Comment: Accepted versio
Spin thermoelectrics in a disordered Fermi gas
We study the connection between the spin-heat and spin-charge response in a
disordered Fermi gas with spin-orbit coupling. It is shown that the ratio
between the above responses can be expressed as the thermopower times a number which depends on the strength and
type of the spin-orbit couplings considered. The general results are
illustrated by examining different two-dimensional electron or hole systems
with different and competing spin-orbit mechanisms, and we conclude that a
metallic system could prove much more efficient as a heat-to-spin than as a
heat-to-charge converter.Comment: 6 pages, 1 figur
Renormalization group and Ward identities in quantum liquid phases and in unconventional critical phenomena
By reviewing the application of the renormalization group to different
theoretical problems, we emphasize the role played by the general symmetry
properties in identifying the relevant running variables describing the
behavior of a given physical system. In particular, we show how the constraints
due to the Ward identities, which implement the conservation laws associated
with the various symmetries, help to minimize the number of independent running
variables. This use of the Ward identities is examined both in the case of a
stable phase and of a critical phenomenon. In the first case we consider the
problems of interacting fermions and bosons. In one dimension general and
specific Ward identities are sufficient to show the non-Fermi-liquid character
of the interacting fermion system, and also allow to describe the crossover to
a Fermi liquid above one dimension. This crossover is examined both in the
absence and presence of singular interaction. On the other hand, in the case of
interacting bosons in the superfluid phase, the implementation of the Ward
identities provides the asymptotically exact description of the acoustic
low-energy excitation spectrum, and clarifies the subtle mechanism of how this
is realized below and above three dimensions. As a critical phenomenon, we
discuss the disorder-driven metal-insulator transition in a disordered
interacting Fermi system. In this case, through the use of Ward identities, one
is able to associate all the disorder effects to renormalizations of the Landau
parameters. As a consequence, the occurrence of a metal-insulator transition is
described as a critical breakdown of a Fermi liquid.Comment: 47 pages, 11 figure
Spin Hall and Edelstein effects in metallic films: from 2D to 3D
A normal metallic film sandwiched between two insulators may have strong
spin-orbit coupling near the metal-insulator interfaces, even if spin-orbit
coupling is negligible in the bulk of the film. In this paper we study two
technologically important and deeply interconnected effects that arise from
interfacial spin-orbit coupling in metallic films. The first is the spin Hall
effect, whereby a charge current in the plane of the film is partially
converted into an orthogonal spin current in the same plane. The second is the
Edelstein effect, in which a charge current produces an in-plane, transverse
spin polarization. At variance with strictly two-dimensional Rashba systems, we
find that the spin Hall conductivity has a finite value even if spin-orbit
interaction with impurities is neglected and "vertex corrections" are properly
taken into account. Even more remarkably, such finite value becomes "universal"
in a certain configuration. This is a direct consequence of the spatial
dependence of spin-orbit coupling on the third dimension, perpendicular to the
film plane. The non-vanishing spin Hall conductivity has a profound influence
on the Edelstein effect, which we show to consist of two terms, the first with
the standard form valid in a strictly two-dimensional Rashba system, and a
second arising from the presence of the third dimension. Whereas the standard
term is proportional to the momentum relaxation time, the new one scales with
the spin relaxation time. Our results, although derived in a specific model,
should be valid rather generally, whenever a spatially dependent Rashba
spin-orbit coupling is present and the electron motion is not strictly
two-dimensional.Comment: 23 pages, 3 figure
Non-linear conductivity and quantum interference in disordered metals
We report on a novel non-linear electric field effect in the conductivity of
disordered conductors. We find that an electric field gives rise to dephasing
in the particle-hole channel, which depresses the interference effects due to
disorder and interaction and leads to a non-linear conductivity. This
non-linear effect introduces a field dependent temperature scale and
provides a microscopic mechanism for electric field scaling at the
metal-insulator transition. We also study the magnetic field dependence of the
non-linear conductivity and suggest possible ways to experimentally verify our
predictions. These effects offer a new probe to test the role of quantum
interference at the metal-insulator transition in disordered conductors.Comment: 5 pages, 3 figure
Current-induced spin polarization and the spin Hall effect: a quasiclassical approach
The quasiclassical Green function formalism is used to describe charge and
spin dynamics in the presence of spin-orbit coupling. We review the results
obtained for the spin Hall effect on restricted geometries. The role of
boundaries is discussed in the framework of spin diffusion equations.Comment: 10 pages, 5 figures, Submitted to Solid State Communications Special
Issue on "Fundamental Phenomena in Low Dimensional Electron Systems". Special
Issue Editors: Marco Polini, Michele Governale, Hermann Grabert, Vittorio
Pellegrini, and Mario Tos
High luminosity interaction region design for collisions with detector solenoid
An innovatory interaction region has been recently conceived and realized on
the Frascati DA{\Phi}NE lepton collider. The concept of tight focusing and
small crossing angle adopted until now to achieve high luminosity in multibunch
collisions has evolved towards enhanced beam focusing at the interaction point
with large horizontal crossing angle, thanks to a new compensation mechanism
for the beam-beam resonances. The novel configuration has been tested with a
small detector without solenoidal field yielding a remarkable improvement in
terms of peak as well as integrated luminosity. The high luminosity interaction
region has now been modified to host a large detector with a strong solenoidal
field which significantly perturbs the beam optics introducing new design
challenges in terms of interaction region optics design, beam transverse
coupling control and beam stay clear requirementsComment: 3 pages, 4 figures, presented to the IPAC10 conferenc
Inverse Spin Hall Effect and Anomalous Hall Effect in a Two-Dimensional Electron Gas
We study the coupled dynamics of spin and charge currents in a
two-dimensional electron gas in the transport diffusive regime. For systems
with inversion symmetry there are established relations between the spin Hall
effect, the anomalous Hall effect and the inverse spin Hall effect. However, in
two-dimensional electron gases of semiconductors like GaAs, inversion symmetry
is broken so that the standard arguments do not apply. We demonstrate that in
the presence of a Rashba type of spin-orbit coupling (broken structural
inversion symmetry) the anomalous Hall effect, the spin Hall and inverse spin
Hall effect are substantially different effects. Furthermore we discuss the
inverse spin Hall effect for a two-dimensional electron gas with Rashba and
Dresselhaus spin-orbit coupling; our results agree with a recent experiment.Comment: 5 page
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