863 research outputs found
Spin and Charge Transport on the Surface of a Topological Insulator
We derive diffusion equations, which describe spin-charge coupled transport
on the helical metal surface of a three-dimensional topological insulator. The
main feature of these equations is a large magnitude of the spin-charge
coupling, which leads to interesting and observable effects. In particular, we
predict a new magnetoresistance effect, which manifests in a nonohmic
correction to a voltage drop between a ferromagnetic spin-polarized electrode
and a nonmagnetic electrode, placed on top of the helical metal. This
correction is proportional to the cross-product of the spin polarization of the
ferromagnetic electrode and the charge current between the two electrodes. We
also demonstrate tunability of this effect by applying a gate voltage, which
makes it possible to operate the proposed device as a transistor.Comment: 4 pages, 1 figure; published versio
Synthesis of high-oxidation Y-Ba-Cu-O phases in superoxygenated thin films
It is known that solid-state reaction in high-pressure oxygen can stabilize
high-oxidation phases of Y-Ba-Cu-O superconductors in powder form. We extend
this superoxygenation concept of synthesis to thin films which, due to their
large surface-to-volume ratio, are more reactive thermodynamically. Epitaxial
thin films of grown by pulsed laser deposition are
annealed at up to 700 atm O and 900C, in conjunction with Cu
enrichment by solid-state diffusion. The films show clear formation of
and as well as regions
of and YBaCuO phases,
according to scanning transmission electron microscopy, x-ray diffraction and
x-ray absorption spectroscopy. Similarly annealed
powders show no phase conversion. Our results demonstrate a novel route of
synthesis towards discovering more complex phases of cuprates and other
superconducting oxides.Comment: Accepted for publication in Physical Review Material
Resonant X-Ray Scattering Measurements of a Spatial Modulation of the Cu 3d and O 2p Energies in Stripe-Ordered Cuprate Superconductors
A prevailing description of the stripe phase in underdoped cuprate
superconductors is that the charge carriers (holes) phase segregate on a
microscopic scale into hole rich and hole poor regions. We report resonant
elastic x-ray scattering measurements of stripe-ordered
LaNdSrCuO at the Cu and O absorption
edges that identify an additional feature of stripe order. Analysis of the
energy dependence of the scattering intensity reveals that the dominant
signature of the stripe order is a spatial modulation in the energies of Cu 3d
and O 2p states rather than the large modulation of the charge density
(valence) envisioned in the common stripe paradigm. These energy shifts are
interpreted as a spatial modulation of the electronic structure and may point
to a valence-bond-solid interpretation of the stripe phase.Comment: 5 pages, 2 figure
Nonvanishing Energy Scales at the Quantum Critical Point of CeCoIn5
Heat and charge transport were used to probe the magnetic field-tuned quantum
critical point in the heavy-fermion metal CeCoIn. A comparison of
electrical and thermal resistivities reveals three characteristic energy
scales. A Fermi-liquid regime is observed below , with both transport
coefficients diverging in parallel and as , the
critical field. The characteristic temperature of antiferromagnetic spin
fluctuations, , is tuned to a minimum but {\it finite} value at ,
which coincides with the end of the -linear regime in the electrical
resistivity. A third temperature scale, , signals the formation of
quasiparticles, as fermions of charge obeying the Wiedemann-Franz law.
Unlike , it remains finite at , so that the integrity of
quasiparticles is preserved, even though the standard signature of Fermi-liquid
theory fails.Comment: 4 pages, 4 figures (published version
Heat Transport as a Probe of Electron Scattering by Spin Fluctuations: the Case of Antiferromagnetic CeRhIn5
Heat and charge conduction were measured in the heavy-fermion metal CeRhIn5,
an antiferromagnet with T_N=3.8 K. The thermal resistivity is found to be
proportional to the magnetic entropy, revealing that spin fluctuations are as
effective in scattering electrons as they are in disordering local moments. The
electrical resistivity, governed by a q^2 weighting of fluctuations, increases
monotonically with temperature. In contrast, the difference between thermal and
electrical resistivities, characterized by an omega^2 weighting, peaks sharply
at T_N and eventually goes to zero at a temperature T^* ~ 8 K. T^* thus emerges
as a measure of the characteristic energy of magnetic fluctuations.Comment: 4 pages, 4 figure
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