8,717 research outputs found
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
Epitaxial Thin Films of the Giant-Dielectric-Constant Material CaCu_3Ti_4O_{12} Grown by Pulsed-laser Deposition
Pulsed-laser deposition has been used to grow epitaxial thin films of the
giant-dielectric-constant material CaCu_3Ti_4O_{12} on LaAlO_3 and SrTiO_3
substrates with or without various conducting buffer layers. The latter include
YBa_2Cu_3O_7, La_{1.85}Sr_{0.15}CuO_{4+\delta} and LaNiO_3. Above 100K - 150K
the thin films have a temperature independent dielectric constant as do single
crystals. The value of the dielectric constant is of the order of 1500 over a
wide temperature region, potentially making it a good candidate for many
applications. The frequency dependence of its dielectric properties below 100K
- 150K indicates an activated relaxation process.Comment: 11 pages, 4 figure
Enhanced flux pinning in YBa2Cu3O7-d films by nano-scaled substrate surface roughness
Nano-scaled substrate surface roughness is shown to strongly influence the
critical current density Jc in YBCO films made by pulse-laser-deposition on the
crystalline LaAlO3 substrates consisting of two separate twin-free and
twin-rich regions. The nano-scaled corrugated surface was created in the
twin-rich region during the deposition process. Using magneto-optical imaging
techniques coupled with optical and atomic force microscopy, we observed an
enhanced flux pinning in the YBCO films in the twin-rich region, resulted in
\~30% increase in Jc, which was unambiguously confirmed by the direct transport
measurement.Comment: 16 pages, 3 figures, accepted by Applied Physics Letter
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
Information dynamics shape the networks of Internet-mediated prostitution
Like many other social phenomena, prostitution is increasingly coordinated
over the Internet. The online behavior affects the offline activity; the
reverse is also true. We investigated the reported sexual contacts between
6,624 anonymous escorts and 10,106 sex-buyers extracted from an online
community from its beginning and six years on. These sexual encounters were
also graded and categorized (in terms of the type of sexual activities
performed) by the buyers. From the temporal, bipartite network of posts, we
found a full feedback loop in which high grades on previous posts affect the
future commercial success of the sex-worker, and vice versa. We also found a
peculiar growth pattern in which the turnover of community members and sex
workers causes a sublinear preferential attachment. There is, moreover, a
strong geographic influence on network structure-the network is geographically
clustered but still close to connected, the contacts consistent with the
inverse-square law observed in trading patterns. We also found that the number
of sellers scales sublinearly with city size, so this type of prostitution does
not, comparatively speaking, benefit much from an increasing concentration of
people
Distinguishing schemes and tasks in children's development of multiplicative reasoning
We present a synthesis of findings from constructivist teaching experiments regarding six schemes children construct for reasoning multiplicatively and tasks to promote them. We provide a task-generating platform game, depictions of each scheme, and supporting tasks. Tasks must be distinguished from childrenâs thinking, and learning situations must be organized to (a) build on childrenâs available schemes, (b) promote the next scheme in the sequence, and (c) link to intended mathematical concepts
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
Spin Transport in a Quantum Wire
We study the effect of electron-electron backscattering interactions on spin
transport in a quantum wire. Even if these interactions have no significant
effect on charge transport, they strongly influence the transport of spin. We
use the quantum Boltzmann equation in the collision approximation to derive
equations of motion for spin current and magnetization. In the limit of small
perturbations from equilibrium, we explain the existence of `precessional' and
`diffusive' behaviors. We also discuss the low-temperature non-linear decay of
an uniform spin current outside the hydrodynamic regime.Comment: 10 pages, 5 figures, REVTE
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