3,579 research outputs found
Spin polarization in the Hubbard model with Rashba spin-orbit coupling on a ladder
The competition between on-site Coulomb repulsion and Rashba spin-orbit
coupling (RSOC) is studied on two-leg ladders by numerical techniques. By
studying persistent currents in closed rings by exact diagonalization, it is
found that the contribution to the current due to the RSOC V_{SO}, for a fixed
value of the Hubbard repulsion U reaches a maximum at intermediate values of
V_{SO}. By increasing the repulsive Hubbard coupling U, this spin-flipping
current is suppressed and eventually it becomes opposite to the spin-conserving
current. The main result is that the spin accumulation defined as the relative
spin polarization between the two legs of the ladder is enhanced by U. Similar
results for this Hubbard-Rashba model are observed for a completely different
setup in which two halves of the ladders are connected to a voltage bias and
the ensuing time-dependent regime is studied by the density
matrix-renormalization group technique. It is also interesting a combined
effect between V_{SO} and U leading to a strong enhancement of
antiferromagnetic order which in turn may explain the observed behavior of the
spin-flipping current. The implications of this enhancement of the spin-Hall
effect with electron correlations for spintronic devices is discussed.Comment: 7 pages, 8 figure
Magnetic and transport signatures of Rashba spin-orbit coupling on the ferromagnetic Kondo lattice model in two dimensions
Motivated by emergent phenomena at oxide surfaces and interfaces,
particularly those involving transition metal oxides with perovskite crystal
structure such as LaTiO3/SrTiO3, we examine the ferromagnetic Kondo lattice
model (FKLM) in the presence of a Rashba spin-orbit coupling (RSOC). Using
numerical techniques, under the assumption that the electrons on localized
orbitals may be treated as classical continuum spins, we compute various
charge, spin and transport properties on square clusters at zero temperature.
We find that the main effect of the RSOC is the destruction of the
ferromagnetic state present in the FKLM at low electron fillings, with the
consequent suppression of conductivity. In addition, near half-filling the RSOC
leads to a departure of the antiferromagnetic state of the FKLM with a
consequent reduction to the intrinsic tendency to electronic phase separation.
The interplay between phase separation on one side, and magnetic and transport
properties on the other, is carefully analyzed as a function of the
RSOC/hopping ratio.Comment: final version, accepted for publication in Phys. Rev.
Shock excitation of the knots of Hen 3-1475
We present new optical STIS HST spectroscopic observations of the jets of the
proto-planetary nebula Hen 3-1475. The excitation conditions of the knots of
Hen 3-1475 are derived from the observed optical spectra, confirming that the
knots are shock excited. The shocked spectra are qualitatively reproduced by
simple ``3/2''D bow shock models. We present a set of bow shock models devoted
to planetary nebulae, and discuss the effects of the pre-ionization conditions,
the bow shock velocity, the bow shock shape and the chemical abundances on the
predicted spectra.
To explore the reliability of the ``3/2''D bow shock models, we also compare
the observed spectra of other three proto-planetary nebulae (M 1-92, M 2-56 and
CRL 618) to the predicted spectra.Comment: 13 pages. A&A (in press
Enhancement of pairing in a boson-fermion model for coupled ladders
Motivated by the presence of various charge inhomogeneities in strongly
correlated systems of coupled ladders, a model of spatially separated bosonic
and fermionic degrees of freedom is numerically studied. In this model, bosonic
chains are connected to fermionic chains by two types of generalized Andreev
couplings. It is shown that for both types of couplings the long-distance
pairing correlations are enhanced. Near quarter filling, this effect is much
larger for the splitting of a pair in electrons which go to the two neighboring
fermionic chains than for a pair hopping process. It is argued that the pairing
enhancement is a result of the nearest neighbor Coulomb repulsion which tunes
the competition between pairing and charge ordering.Comment: 7 pages, 7 eps figures, enlarged version accpeted in Phys. Rev.
- …