1,073 research outputs found
Competing types of quantum oscillations in the 2D organic conductor (BEDT-TTF)8Hg4Cl12(C6H5Cl)2
Interlayer magnetoconductance of the quasi-two dimensional organic metal
(BEDT-TTF)8Hg4Cl12(C6H5Cl)2 has been investigated in pulsed magnetic fields
extending up to 36 T and in the temperature range from 1.6 to 15 K. A complex
oscillatory spectrum, built on linear combinations of three basic frequencies
only is observed. These basic frequencies arise from the compensated closed
hole and electron orbits and from the two orbits located in between. The field
and temperature dependencies of the amplitude of the various oscillation series
are studied within the framework of the coupled orbits model of Falicov and
Stachowiak. This analysis reveals that these series result from the
contribution of either conventional Shubnikov-de Haas effect (SdH) or quantum
interference (QI), both of them being induced by magnetic breakthrough.
Nevertheless, discrepancies between experimental and calculated parameters
indicate that these phenomena alone cannot account for all of the data. Due to
its low effective mass, one of the QI oscillation series - which corresponds to
the whole first Brillouin zone area - is clearly observed up to 13 K.Comment: 8 pages, 8 figures. To be published in Phys. Rev.
Evidence for a new magnetic field scale in CeCoIn5
The Nernst coefficient of CeCoIn5 displays a distinct anomaly at H_K ~ 23 T.
This feature is reminiscent of what is observed at 7.8 T in CeRu2Si2, a
well-established case of metamagnetic transition. New frequencies are observed
in de Haas-van Alphen oscillations when the field exceeds 23 T, which may
indicate a modification of the Fermi surface at this field.Comment: submitted to Physical Review Letter
Heat transport in Bi_{2+x}Sr_{2-x}CuO_{6+\delta}: departure from the Wiedemann-Franz law in the vicinity of the metal-insulator transition
We present a study of heat transport in the cuprate superconductor
Bi_{2+x}Sr_{2-x}CuO_{6+\delta} at subkelvin temperatures and in magnetic fields
as high as 25T. In several samples with different doping levels close to
optimal, the linear-temperature term of thermal conductivity was measured both
at zero-field and in presence of a magnetic field strong enough to quench
superconductivity. The zero-field data yields a superconducting gap of
reasonable magnitude displaying a doping dependence similar to the one reported
in other families of cuprate. The normal-state data together with the results
of the resistivity measurements allows us to test the Wiedemann-Franz(WF) law,
the validity of which was confirmed in an overdoped sample in agreement with
previous studies. In contrast, a systematic deviation from the WF law was
resolved for samples displaying either a lower doping content or a higher
disorder. Thus, in the vicinity of the metal-insulator cross-over, heat
conduction in the zero-temperature limit appears to become significantly larger
than predicted by the WF law. Possible origins of this observation are
discussed.Comment: 9 pages including 7 figures, submitted to Phys. Rev.
Action of Humicola lanuginosa lipase on mixed monomolecular films of tricaprylin and polyethylene glycol stearate
The hydrolysis catalyzed by Humicola lanuginosa lipase (HLL) of pure tricaprylin (TC) or stearate of polyethylene glycol 1500 (PEG-St) as well as their mixtures spread as monomolecular films were studied. The catalytic transformation of the two substrates TC or PEG-St into their respective reaction products was detected by measuring simultaneously the decrease in the film area and the surface potential using the "zero order" trough at constant surface pressure. A kinetic model describing the enzymatic hydrolysis was developed. The surface concentrations of the two substrates and their respective reaction products as well as the values of the global kinetic constants of hydrolysis were determined. The experimentally obtained global kinetic constants of the catalytic action of HLL against TC and PEG-St present in mixed monolayers of TC/PEG-St are approximately the same as in the case of pure monolayers. These obtained results give some indications that the activity of enzyme is not significantly affected by the different molecular environments in the mixed monolayers
Structure and dynamics of the Shapley Supercluster
We present results of our wide-field redshift survey of galaxies in a 285
square degree region of the Shapley Supercluster (SSC), based on a set of 10529
velocity measurements (including 1201 new ones) on 8632 galaxies obtained from
various telescopes and from the literature. Our data reveal that the main plane
of the SSC (v~ 14500 km/s) extends further than previous estimates, filling the
whole extent of our survey region of 12~degrees by 30~degrees on the sky (30 x
75~h-1 Mpc). There is also a connecting structure associated with the slightly
nearer Abell~3571 cluster complex (v~ 12000km/s. These galaxies seem to link
two previously identified sheets of galaxies and establish a connection with a
third one at V= 15000 km/s near R.A.= 13h. They also tend to fill the gap of
galaxies between the foreground Hydra-Centaurus region and the more distant
SSC. In the velocity range of the Shapley Supercluster (9000 km/s < cz < 18000
km/s), we found redshift-space overdensities with b\_j < 17.5 of ~5.4 over the
225 square degree central region and ~3.8 in a 192 square degree region
excluding rich clusters. Over the large region of our survey, we find that the
intercluster galaxies make up 48 per cent of the observed galaxies in the SSC
region and, accounting for the different completeness, may contribute nearly
twice as much mass as the cluster galaxies. In this paper, we discuss the
completeness of the velocity catalogue, the morphology of the supercluster, the
global overdensity, and some properties of the individual galaxy clusters in
the Supercluster.Comment: Accepted for publication in Astronomy and Astrophysic
Fermi Surface of the Electron-doped Cuprate Superconductor Nd_{2-x}Ce_xCuO_{4} Probed by High-Field Magnetotransport
We report on the study of the Fermi surface of the electron-doped cuprate
superconductor NdCeCuO by measuring the interlayer
magnetoresistance as a function of the strength and orientation of the applied
magnetic field. We performed experiments in both steady and pulsed magnetic
fields on high-quality single crystals with Ce concentrations of to
0.17. In the overdoped regime of we found both semiclassical
angle-dependent magnetoresistance oscillations (AMRO) and Shubnikov-de Haas
(SdH) oscillations. The combined AMRO and SdH data clearly show that the
appearance of fast SdH oscillations in strongly overdoped samples is caused by
magnetic breakdown. This observation provides clear evidence for a
reconstructed multiply-connected Fermi surface up to the very end of the
overdoped regime at . The strength of the superlattice potential
responsible for the reconstructed Fermi surface is found to decrease with
increasing doping level and likely vanishes at the same carrier concentration
as superconductivity, suggesting a close relation between translational
symmetry breaking and superconducting pairing. A detailed analysis of the
high-resolution SdH data allowed us to determine the effective cyclotron mass
and Dingle temperature, as well as to estimate the magnetic breakdown field in
the overdoped regime.Comment: 23 pages, 8 figure
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