251 research outputs found
Spin Hall Drag
We predict a new effect in electronic bilayers: the {\it Spin Hall Drag}. The
effect consists in the generation of spin accumulation across one layer by an
electric current along the other layer. It arises from the combined action of
spin-orbit and Coulomb interactions. Our theoretical analysis, based on the
Boltzmann equation formalism, identifies two main contributions to the spin
Hall drag resistivity: the side-jump contribution, which dominates at low
temperature, going as , and the skew-scattering contribution, which is
proportional to . The induced spin accumulation is large enough to be
detected in optical rotation experiments.Comment: 5 pages, 2 figure
Sub-threshold resonances in few-neutron systems
Three- and four-neutron systems are studied within the framework of the
hyperspherical approach with a local S-wave nn-potential. Possible bound and
resonant states of these systems are sought as zeros of three- and four-body
Jost functions in the complex momentum plane. It is found that zeros closest to
the origin correspond to sub-threshold (nnn) (1/2-) and (nnnn) (0+) resonant
states. The positions of these zeros turned out to be sensitive to the choice
of the --potential. For the Malfliet- Tjon potential they are
E(nnn)=-4.9-i6.9 (MeV) and E(nnnn)=-2.6-i9.0 (MeV). Movement of the zeros with
an artificial increase of the potential strength also shows an extreme
sensitivity to the choice of potential. Thus, to generate ^3n and ^4n bound
states, the Yukawa potential needs to be multiplied by 2.67 and 2.32
respectively, while for the Malfliet-Tjon potential the required multiplicative
factors are 4.04 and 3.59.Comment: Latex, 22 pages, no PS-figures, submitted to J.Phys.
Compact and Loosely Bound Structures in Light Nuclei
A role of different components in the wave function of the weakly bound light
nuclei states was studied within the framework of the cluster model, taking
into account of orbitals "polarization". It was shown that a limited number of
structures associated with the different modes of nucleon motion can be of
great importance for such systems. Examples of simple and quite flexible trial
wave functions are given for the nuclei Be, He. Expressions for the
microscopic wave functions of these nuclei were found and used for the
calculation of basic nuclear characteristics, using well known central-exchange
nucleon-nucleon potentials.Comment: 19 pages, 3 ps figure
Inhomogeneity of the intrinsic magnetic field in superconducting YBa2Cu3OX compounds as revealed by rare-earth EPR-probe
X-band electron paramagnetic resonance on doped Er3+ and Yb3+ ions in
Y0.99(Yb,Er)0.01Ba2Cu3OX compounds with different oxygen contents in the wide
temperature range (4-120)K have been made. In the superconducting species, the
strong dependencies of the linewidth and resonance line position from the sweep
direction of the applied magnetic field are revealed at the temperatures
significantly below TC. The possible origins of the observed hysteresis are
analyzed. Applicability of the presented EPR approach to extract information
about the dynamics of the flux-line lattice and critical state parameters
(critical current density, magnetic penetration depth, and characteristic
spatial scale of the inhomogeneity) is discussedComment: 17 pages, 5 Figures. Renewed versio
Hyperon-Nucleon Final State Interaction in Kaon Photoproduction of the Deuteron
Final state hyperon-nucleon interaction in strangeness photoproduction of the
deuteron is investigated making use of the covariant reaction formalism and the
P-matrix approach to the YN system. Remarkably simple analytical expression for
the amplitude is obtained. Pronounced effects due to final state interaction
are predicted including the manifestation of the 2.13 GeV resonance.Comment: LaTeX, 13 page
Missing 2k_F Response for Composite Fermions in Phonon Drag
The response of composite Fermions to large wavevector scattering has been
studied through phonon drag measurements. While the response retains
qualitative features of the electron system at zero magnetic field, notable
discrepancies develop as the system is varied from a half-filled Landau level
by changing density or field. These deviations, which appear to be inconsistent
with the current picture of composite Fermions, are absent if half-filling is
maintained while changing density. There remains, however, a clear deviation
from the temperature dependence anticipated for 2k_F scattering.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. Let
Surface acoustic wave attenuation by a two-dimensional electron gas in a strong magnetic field
The propagation of a surface acoustic wave (SAW) on GaAs/AlGaAs
heterostructures is studied in the case where the two-dimensional electron gas
(2DEG) is subject to a strong magnetic field and a smooth random potential with
correlation length Lambda and amplitude Delta. The electron wave functions are
described in a quasiclassical picture using results of percolation theory for
two-dimensional systems. In accordance with the experimental situation, Lambda
is assumed to be much smaller than the sound wavelength 2*pi/q. This restricts
the absorption of surface phonons at a filling factor \bar{\nu} approx 1/2 to
electrons occupying extended trajectories of fractal structure. Both
piezoelectric and deformation potential interactions of surface acoustic
phonons with electrons are considered and the corresponding interaction
vertices are derived. These vertices are found to differ from those valid for
three-dimensional bulk phonon systems with respect to the phonon wave vector
dependence. We derive the appropriate dielectric function varepsilon(omega,q)
to describe the effect of screening on the electron-phonon coupling. In the low
temperature, high frequency regime T << Delta (omega_q*Lambda
/v_D)^{alpha/2/nu}, where omega_q is the SAW frequency and v_D is the electron
drift velocity, both the attenuation coefficient Gamma and varepsilon(omega,q)
are independent of temperature. The classical percolation indices give
alpha/2/nu=3/7. The width of the region where a strong absorption of the SAW
occurs is found to be given by the scaling law |Delta \bar{\nu}| approx
(omega_q*Lambda/v_D)^{alpha/2/nu}. The dependence of the electron-phonon
coupling and the screening due to the 2DEG on the filling factor leads to a
double-peak structure for Gamma(\bar{\nu}).Comment: 17 pages, 3 Postscript figures, minor changes mad
Coupled-channel effective field theory and proton-Li scattering
We apply the renormalisation group (RG) to analyse scattering by short-range
forces in systems with coupled channels. For two S-wave channels, we find three
fixed points, corresponding to systems with zero, one or two bound or virtual
states at threshold. We use the RG to determine the power countings for the
resulting effective field theories. In the case of a single low-energy state,
the resulting theory takes the form of an effective-range expansion in the
strongly interacting channel. We also extend the analysis to include the
effects of the Coulomb interaction between charged particles. The approach is
then applied to the coupled Li and Be channels which couple to
a state of Be very close to the Be threshold. At
next-to-leading order, we are able to get a good description of the Li
phase shift and the Be(n,p)Li cross section using four parameters.
Fits at one order higher are similarly good but the available data are not
sufficient to determine all five parameters uniquely.Comment: 22 pages, 2 figures, RevTeX4, typos corrected, accepted for
publication in European Physical Journal
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