36 research outputs found
Antiferromagnetic Alignment and Relaxation Rate of Gd Spins in the High Temperature Superconductor GdBa_2Cu_3O_(7-delta)
The complex surface impedance of a number of GdBaCuO
single crystals has been measured at 10, 15 and 21 GHz using a cavity
perturbation technique. At low temperatures a marked increase in the effective
penetration depth and surface resistance is observed associated with the
paramagnetic and antiferromagnetic alignment of the Gd spins. The effective
penetration depth has a sharp change in slope at the N\'eel temperature, ,
and the surface resistance peaks at a frequency dependent temperature below 3K.
The observed temperature and frequency dependence can be described by a model
which assumes a negligibly small interaction between the Gd spins and the
electrons in the superconducting state, with a frequency dependent magnetic
susceptibility and a Gd spin relaxation time being a strong function
of temperature. Above , has a component varying as , while below it increases .Comment: 4 Pages, 4 Figures. Submitted to Phys. Rev.
Non-Locality and Strong Coupling in the Heavy Fermion Superconductor CeCoIn: A Penetration Depth Study
We report measurements of the magnetic penetration depth in single
crystals of CeCoIn down to 0.14 K using a tunnel-diode based,
self-inductive technique at 28 MHz. While the in-plane penetration depth tends
to follow a power law, , the data are better
described as a crossover between linear ({\it T} ) and
quadratic ({\it T} ) behavior, with the
crossover temperature in the strong-coupling limit. The {\it c}-axis
penetration depth is linear in {\it T}, providing evidence
that CeCoIn is a {\it d}-wave superconductor with line nodes along the
{\it c}-axis. The different temperature dependences of and
rule out impurity effects as the source of .Comment: 4 pages, 3 figure
Transcriptome pathways unique to dehydration tolerant relatives of modern wheat
Among abiotic stressors, drought is a major factor responsible for dramatic yield loss in agriculture. In order to reveal differences in global expression profiles of drought tolerant and sensitive wild emmer wheat genotypes, a previously deployed shock-like dehydration process was utilized to compare transcriptomes at two time points in root and leaf tissues using the Affymetrix GeneChip(R) Wheat Genome Array hybridization. The comparison of transcriptomes reveal several unique genes or expression patterns such as differential usage of IP(3)-dependent signal transduction pathways, ethylene- and abscisic acid (ABA)-dependent signaling, and preferential or faster induction of ABA-dependent transcription factors by the tolerant genotype that distinguish contrasting genotypes indicative of distinctive stress response pathways. The data also show that wild emmer wheat is capable of engaging known drought stress responsive mechanisms. The global comparison of transcriptomes in the absence of and after dehydration underlined the gene networks especially in root tissues that may have been lost in the selection processes generating modern bread wheats
Volatile diterpene emission by two Mediterranean Cistaceae shrubs
Mediterranean vegetation emits a wide range of biogenic volatile organic compounds (BVOCs) among
which isoprenoids present quantitatively the most important compound class. Here, we investigated
the isoprenoid emission from two Mediterranean Cistaceae shrubs, Halimium halimifolium and Cistus
ladanifer, under controlled and natural conditions, respectively. For the first time, diurnal emission
patterns of the diterpene kaurene were detected in real-time by Proton-Transfer-Reaction-Timeof-
Flight-Mass-Spectrometer. Kaurene emissions were strongly variable among H. halimifolium
plants, ranging from 0.01 ± 0.003 to 0.06 ± 0.01 nmol m−2 s−1 in low and high emitting individuals,
respectively. They were in the same order of magnitude as monoterpene (0.01 ± 0.01 to 0.11 ± 0.04
nmol m−2 s−1) and sesquiterpene (0.01 ± 0.01 to 0.52 nmol m−2 s−1) emission rates. Comparable
range and variability was found for C. ladanifer under natural conditions. Labelling with 13C-pyruvate
suggested that emitted kaurene was not derived from de novo biosynthesis. The high kaurene content
in leaves, the weak relationship with ecophysiological parameters and the tendency of higher emissions
with increasing temperatures in the field indicate an emission from storage pools. This study highlights
significant emissions of kaurene from two Mediterranean shrub species, indicating that the release of
diterpenes into the atmosphere should probably deserve more attention in the futureinfo:eu-repo/semantics/publishedVersio
In-plane microwave conductivity of the single-layer cuprate Tl<sub>2</sub>Ba<sub>2</sub>CuO<sub>6+δ</sub>
We have measured the in-plane microwave conductivity of nearly optimally doped single crystals (Tc=78 K) of Tl2Ba2CuO6+δ (Tl-2201) at 14.4, 24.8, and 35.9 GHz using cavity perturbation methods. At low temperatures, the in-plane penetration depth has a strong, linear temperature dependence, indicative of an unconventional pairing state with line nodes. The real part of the conductivity shows a broad, frequency-dependent peak near 30 K, similar to that seen in YBa2Cu3O7-δ and Bi2Sr2CaCu2O8 crystals. With tetragonal crystal symmetry and a single CuO2 plane per unit cell, Tl-2201 is the simplest structure so far to display these features
ab-Plane surface impedance of the single-layer cuprate Tl<sub>2</sub>Ba<sub>2</sub>CuO<sub>6+δ</sub>
The ab-plane surface impedance of Tl2Ba2CuO6+δ (Tl-2201) has been measured at 14.4, 24.8 and 35.9 GHz using cavity perturbation techniques. The result of these measurements is a picture of the superconducting electrodynamics of Tl-2201 that closely resembles those of YBa2Cu3O7−δ and Bi2Sr2CaCu2O8. Here we describe the main features of our measurements; in particular, we see a linear temperature dependence of the in-plane penetration depth at low temperature, consistent with an unconventional pairing state with line nodes. The simple crystal structure of Tl-2201 (tetragonal, with a single CuO2 plane/unit cell) makes this an interesting addition to our knowledge of cuprate electrodynamics