1,645 research outputs found
Rashba splitting of Cooper pairs
We investigate theoretically the properties of a weak link between two
superconducting leads, which has the form of a non-superconducting nanowire
with a strong Rashba spin-orbit coupling caused by an electric field. In the
Coulomb blockade regime of single-electron tunneling, we find that such a weak
link acts as a "spin splitter" of the spin states of Cooper pairs tunneling
through the link, to an extent that depends on the direction of the electric
field. We show that the Josephson current is sensitive to interference between
the resulting two transmission channels, one where the spins of both members of
a Cooper pair are preserved and one where they are both flipped. As a result,
the current is a periodic function of the strength of the spin-orbit
interaction and of the bending angle of the nanowire (when mechanically bent);
an identical effect appears due to strain-induced spin-orbit coupling. In
contrast, no spin-orbit induced interference effect can influence the current
through a single weak link connecting two normal metals.Comment: 5 pages 3 figures. arXiv admin note: text overlap with
arXiv:1306.512
Evolution of the universality class in slightly diluted (1>p>0.8) Ising systems
The crossover of a pure (undiluted) Ising system (spin per site probability
p=1) to a diluted Ising system (spin per site probability p<0.8) is studied by
means of Monte Carlo calculations with p ranging between 1 and 0.8 at intervals
of 0.025. The evolution of the self averaging is analyzed by direct
determination of the normalized square widths for magnetization and
susceptibility as a function of p. We find a monotonous and smooth evolution
from the pure to the randomly diluted universality class. The p-dependent
transition is found to be independent of the size (L). This property is very
convenient for extrapolation towards the randomly diluted universality class
avoiding complications resulting from finite size effects.Comment: 15 pages, 6 figures, RevTe
Comment on "Strong dependence of the interlayer coupling on the hole mobility in antiferromagnetic LaSrCuO ()"
Using the experimental data given in Phys. Rev. B70, 220507 (2004), we show
that -- unlike the effective coupling discussed in this paper -- the net
average antiferromagnetic interlayer coupling in doped lanthanum cuprates
depends only weakly on the doping or on the temperature. We argue that the
effective coupling is proportional to the square of the staggered
magnetization, and does not supply new information about the origin of the
suppression of the magnetic order in doped samples. Our analysis is based on a
modified version of the equation describing the spin-flip transition, which
takes into account the decrease of the staggered moment with temperature and
doping.Comment: Phys. Rev. B (in press
Unusual Symmetries in the Kugel-Khomskii Hamiltonian
The Kugel-Khomskii Hamiltonian for cubic titanates describes spin and orbital
superexchange interactions between ions having three-fold degenerate
orbitals. Since orbitals do not couple along "inactive" axes,
perpendicular to the orbital planes, the total number of electrons in orbitals in any such plane and the corresponding total spin are both
conserved. A Mermin-Wagner construction shows that there is no long-range spin
ordering at nonzero temperatures. Inclusion of spin-orbit coupling allows such
ordering, but even then the excitation spectrum is gapless due to a continuous
symmetry. Thus, the observed order and gap require more symmetry breaking
terms.Comment: 4 pages (two column format with 2 figures), to appear in Phys. Rev.
Lett. (submitted on Dec. 2002
Suppression of antiferromagnetic correlations by quenched dipole--type impurities
The effect of quenched random ferromagnetic bonds on the antiferromagnetic
correlation length of a two--dimensional Heisneberg model is studied, applying
the renormalization group method to the classical non--linear sigma model with
quenched random dipole moments. It is found that the antiferromagnetic long
range order is destroyed for any non--zero concentration, of the dipolar
defects, even at zero temperature. Below a line T ~ concentration, the
correlation length is independent of T, and decreases exponentially with
concentration. At higher temperatures, itdecays exponentially with an effective
stiffness constant which decreases with concentration/T. The results are used
to estimate the three--dimensional N\'{e}el temperature, which decays linearly
with at small concentrations, and drops precipitously at a critical
concentration. These predictions are compared with experiments on doped copper
oxides, and are shown to reproduce successfully some of the prominent features
of the data.Comment: 34 pages, LateX, 4 figures Rport-no: TAU
Rashba proximity states in superconducting tunnel junctions
We consider a new kind of superconducting proximity effect created by the
tunneling of "spin split" Cooper pairs between two conventional superconductors
connected by a normal conductor containing a quantum dot. The difference
compared to the usual superconducting proximity effect is that the spin states
of the tunneling Cooper pairs are split into singlet and triplet components by
the electron spin-orbit coupling, which is assumed to be active in the normal
conductor only. We demonstrate that the supercurrent carried by the spin-split
Cooper pairs can be manipulated both mechanically and electrically for
strengths of the spin-orbit coupling that can realistically be achieved by
electrostatic gates.Comment: Accepted for publication in Fiz. Niz. Temp./Low Temp. Phys. vol. 44,
no. 6, 2018. arXiv admin note: text overlap with arXiv:1709.0802
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