54 research outputs found
Heat transport and spin-charge separation in the normal state of high temperature superconductors
Hill et al. have recently measured both the thermal and charge conductivities
in the normal state of a high temperature superconductor. Based on the
vanishing of the Wiedemann-Franz ratio in the extrapolated zero temperature
limit, they conclude that the charge carriers in this material are not
fermionic. Here I make a simple observation that the prefactor in the
temperature dependence of the measured thermal conductivity is unusually large,
corresponding to an extremely small energy scale K. I argue
that should be interpreted as a collective scale. Based on
model-independent considerations, I also argue that the experiment leads to two
possibilities: 1) The charge-carrying excitations are non-fermionic. And much
of the heat current is in fact carried by distinctive charge-neutral
excitations; 2) The charge-carrying excitations are fermionic, but a subtle
ordering transition occurs at .Comment: 3 pages, 1 figur
Probing spin-charge separation using spin transport
Pedagogical discussions are given on what constitutes a signature of
spin-charge separation. A proposal is outlined to probe spin-charge separation
in the normal state of the high cuprates using spin transport.
Specifically, the proposal is to compare the temperature dependences of the
spin resistivity and electrical resistivity: Spin-charge separation will be
manifested in the different temperature dependences of these two resistivities.
We also estimate the spin diffusion length and spin relaxation time scales, and
we argue that it should be experimentally feasible to measure the spin
transport properties in the cuprates using the spin-injection technique. The
on-going spin-injection experiments in the cuprates and related theoretical
issues are also discussed.Comment: Talk given at M2S-HTSC-VI, 4 page
Spin current and polarization in impure 2D electron systems with spin-orbit coupling
We derive the transport equations for two-dimensional electron systems with
spin-orbit interaction and short-range spin-independent disorder. In the limit
of slow spatial variations of the electron distribution we obtain coupled
diffusion equations for the electron density and spin. Using these equations we
calculate electric-field induced spin accumulation in a finite-size sample for
arbitrary ratio between spin-orbit energy splitting and elastic scattering
rate. We demonstrate that the spin-Hall conductivity vanishes in an infinite
system independent of this ratio.Comment: 5 pages, 1 figure; revised version according to referee's commment
Spin orientation by electric current in (110) quantum wells
We develop a theory of spin orientation by electric current in (110)-grown
semiconductor quantum wells. The controversy in the factor of two from two
existed approaches is resolved by pointing out the importance of energy
relaxation in this problem. The limiting cases of fast and slow energy
relaxation relative to spin relaxation are considered for asymmetric (110)
quantum wells. For symmetricly-doped structures the effect of spin orientation
is shown to exist due to spatial fluctuations of the Rashba spin-orbit
splitting. We demonstrate that the spin orientation depends strongly on the
correlation length of these fluctuations as well as on the ratio of the energy
and spin relaxation rates. The time-resolved kinetics of spin polarization by
electric current is also governed by the correlation length being not purely
exponential at slow energy relaxation. Electrical spin orientation in
two-dimensional topological insulators is calculated and compared with the spin
polarization induced by the magnetic field.Comment: 8 pages, 2 figure
Правовая природа административного трибунала Совета Европы
Васько Е. А. Правовая природа административного трибунала Совета Европы / Е. А. Васько // Міжнародні читання з міжнародного права пам’яті професора П. Є. Казанського : матеріали четвертої міжнар. наук. конф. (м. Одеса, 8–9 лист. 2013 р.) / відп. за випуск к.ю.н., доц. М. І. Пашковський; Національний університет "Одеська юридична академія". – Одеса : Фенікс, 2013. – С. 516-520
Spin-polarized tunneling of La0.67Sr0.33MnO3/YBa2Cu3O7-d junctions
The transport properties between ferromagnets and high-Tc superconductors are
investigated in La0.67Sr0.33MnO3/YBa2Cu3O7-d (LSMO/YBCO)junctions in the
geometry of cross-strip lines. The conductance spectra show zero-bias
conductance peaks (ZBCP), reflecting the charge transport in the ab-plane. When
an external magnetic field is applied to the junctions, the conductance spectra
show two notable features, i.e., an increase of background conductance and an
asymmetric ZBCP splitting whose amplitude responds nonlinearly to the applied
field. It is shown that the magnetic field response are consistent with a
theoretical prediction of tunneling spectroscopy when the presence of a
ferromagnetic barrier between a spin-polarized ferromagnet and a d-wave
superconductor is assumed.Comment: 10 Pages, 7 EPS figures, Submitted to Phys. Rev.
Andreev Reflection and Spin Injection into and wave Superconductors
We study the effect of spin injection into and wave superconductors,
with an emphasis on the interplay between boundary and bulk spin transport
properties. The quantities of interest include the amount of non-equilibrium
magnetization (), as well as the induced spin-dependent current () and
boundary voltage (). In general, the Andreev reflection makes each of the
three quantities depend on a different combination of the boundary and bulk
contributions. The situation simplifies either for half-metallic ferromagnets
or in the strong barrier limit, where both and depend solely on the
bulk spin transport/relaxation properties. The implications of our results for
the on-going spin injection experiments in high cuprates are discussed.Comment: 4 pages, REVTEX, 1 figure included; typos correcte
Suppression of Superconductivity in YBCO/LCMO Superlattices
The competition of superconductivity and magnetism in superlattices composed
of alternating YBaCuO and LaCaMnO thin
films is investigated using low-energy optical spectroscopy. The thickness of
the superconducting YBCO layers is varied from 30 nm to 20 nm while the
thickness of the magnetic LCMO layers is kept constant at 20 nm. We clearly
observe that the superconducting condensate density in the superconducting
state of superlattice is drastically reduced by the magnetic subsystem which
may be connected with proximity effects that distort the gap symmetry and thus
suppress superconductivity.Comment: 4 pages, 4 figure
Spin-orbit interaction in three-dimensionally bounded semiconductor nanostructures
The structural inversion asymmetry-induced spin-orbit interaction of
conduction band electrons in zinc-blende and wurtzite semiconductor structures
is analysed allowing for a three-dimensional (3D) character of the external
electric field and variation of the chemical composition. The interaction,
taking into account all remote bands perturbatively, is presented with two
contributions: a heterointerface term and a term caused by the external
electric field. They have generally comparable strength and can be written in a
unified manner only for 2D systems, where they can partially cancel each other.
For quantum wires and dots composed of wurtzite semiconductors new terms
appear, absent in zinc-blende structures, which acquire the standard Rashba
form in 2D systems.Comment: 18 pages, 1 figur
Spin Injection into a Luttinger Liquid
We study the effect of spin injection into a Luttinger liquid. The
spin-injection-detection setup of Johnson and Silsbee is considered; here spins
injected into the Luttinger liquid induce, across an interface with a
ferromagnetic metal, either a spin-dependent current () or a
spin-dependent boundary voltage (). We find that the spin-charge
separation nature of the Luttinger liquid affects and in a very
different fashion. In particular, in the Ohmic regime, depends on the
spin transport properties of the Luttinger liquid in essentially the same way
as it would in the case of a Fermi liquid. The implications of our results for
the spin-injection-detection experiments in the high cuprates are
discussed.Comment: 4 pages, REVTEX, 2 figures. Minor changes and corrections to typos.
To appear in Phys. Rev. Let
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