30 research outputs found
Epitaxy and magnetotransport of Sr_2FeMoO_6 thin films
By pulsed-laser deposition epitaxial thin films of Sr_2FeMoO_6 have been pre-
pared on (100) SrTiO_3 substrates. Already for a deposition temperature of 320
C epitaxial growth is achieved. Depending on deposition parameters the films
show metallic or semiconducting behavior. At high (low) deposition temperature
the Fe,Mo sublattice has a rock-salt (random) structure. The metallic samples
have a large negative magnetoresistance which peaks at the Curie temperature.
The magnetic moment was determined to 4 mu_B per formula unit (f.u.), in
agreement with the expected value for an ideal ferrimagnetic arrangement. We
found an ordinary Hall coefficient of -6.01x10^{-10} m^3/As at 300 K,
corresponding to an electronlike charge-carrier density of 1.3 per Fe,Mo-pair.
In the semiconducting films the magnetic moment is reduced to 1 mu_B/f.u. due
to disorder in the Fe,Mo sublattice. In low fields an anomalous holelike
contribution dominates the Hall voltage, which vanishes at low temperatures for
the metallic films only.Comment: Institute of Physics, University of Mainz, Germany, 4 pages,
including 5 pictures and 1 Table, submitted to Phys. Rev.
Experimental Test of the Inter-Layer Pairing Models for High-Tc Superconductivity Using Grazing Incidence Infrared Reflectometry
From measurements of the far-infrared reflectivity at grazing angles of
incidence with p-polarized light we determined the c-axis Josephson plasma
frequencies of the single layer high T_c cuprates Tl_2Ba_2CuO_6 and
La_{2-x}Sr_xCuO_4. We detected a strong plasma resonance at 50 cm^{-1} for
La_{2-x}Sr_xCuO_4 in excellent agreement with previously published results. For
Tl_2Ba_2CuO_6 we were able to determine an upper limit of the unscreened c-axis
Josephson plasma frequency 100 cm^{-1} or a c-axis penetration depth > 15 \mu
m. The small value of stands in contrast to recent a prediction
based on the inter-layer tunneling mechanism of superconductivity.Comment: 4 pages, Phys. Rev. B, in press, Revtex, 4 postscript figure
Superconducting Magnetization above the Irreversibility Line in Tl2Ba2CuO6
Piezolever torque magnetometry has been used to measure the magnetization of
superconducting Tl2Ba2CuO6. Three crystals with different levels of oxygen
overdoping were investigated in magnetic fields up to 10 Tesla. In all cases,
the magnetization above the irreversibility line was found to depart from the
behaviour M ~ ln(Hc2/H) of a simple London-like vortex liquid. In particular,
for a strongly overdoped (Tc = 15K) crystal, the remnant superconducting order
above the irreversibility line is characterized by a linear diamagnetic
response (M ~ H) that persists well above Tc and also up to the highest field
employed.Comment: RevTeX, 11 pages, 7 encapsulated PostScript figures, submitted to
Physical Review
Correlated local distortions of the TlO layers in TlBaCuO: An x-ray absorption study
We have used the XAFS (x-ray-absorption fine structure) technique to
investigate the local structure about the Cu, Ba, and Tl atoms in orthorhombic
Tl-2201 with a superconducting transition temperature T=60 K. Our results
clearly show that the O(1), O(2), Cu, and Ba atoms are at their ideal sites as
given by the diffraction measurements, while the Tl and O(3) atoms are more
disordered than suggested by the average crystal structure. The Tl-Tl distance
at 3.5 \AA{ } between the TlO layers does not change, but the Tl-Tl distance at
3.9 \AA{ } within the TlO layer is not observed and the Tl-Ba and Ba-Tl peaks
are very broad. The shorter Tl-O(3) distance in the TlO layer is about 2.33
\AA, significantly shorter than the distance calculated with both the Tl and
O(3) atoms at their ideal sites ( 0 or ). A model based
on these results shows that the Tl atom is displaced along the
directions from its ideal site by about 0.11 \AA; the displacements of
neighboring Tl atoms are correlated. The O(3) atom is shifted from the $4e$
site by about 0.53 \AA{ } roughly along the directions. A comparison of
the Tl L-edge XAFS spectra from three samples, with T=60 K, 76 K,
and 89 K, shows that the O environment around the Tl atom is sensitive to T
while the Tl local displacement is insensitive to T and the structural
symmetry. These conclusions are compared with other experimental results and
the implications for charge transfer and superconductivity are discussed. This
paper has been submitted to Phys. Rev. B.Comment: 20 pages plus 14 ps figures, REVTEX 3.
Epitaxial Structure of (001)- and (111)-Oriented Perovskite Ferrate Films Grown by Pulsed-Laser Deposition
A manually annotated Actinidia chinensis var. chinensis (kiwifruit) genome highlights the challenges associated with draft genomes and gene prediction in plants
Most published genome sequences are drafts, and most are dominated by computational gene prediction. Draft genomes typically incorporate considerable sequence data that are not assigned to chromosomes, and predicted genes without quality confidence measures. The current Actinidia chinensis (kiwifruit) 'Hongyang' draft genome has 164\ua0Mb of sequences unassigned to pseudo-chromosomes, and omissions have been identified in the gene models
Organic Superconductors: when correlations and magnetism walk in
This survey provides a brief account for the start of organic
superconductivity motivated by the quest for high Tc superconductors and its
development since the eighties'. Besides superconductivity found in 1D organics
in 1980, progresses in this field of research have contributed to better
understand the physics of low dimensional conductors highlighted by the wealth
of new remarkable properties. Correlations conspire to govern the low
temperature properties of the metallic phase. The contribution of
antiferromagnetic fluctuations to the interchain Cooper pairing proposed by the
theory is borne out by experimental investigations and supports
supercondutivity emerging from a non Fermi liquid background. Quasi one
dimensional organic superconductors can therefore be considered as simple
prototype systems for the more complex high Tc materials.Comment: 41 pages, 21 figures to be published in Journal of Superconductivity
and Novel Magnetis