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Search Results: 1 - 10 of 297438 matches for " J. Leotin "
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Infrared study of spin-Peierls compound alpha'-NaV2O5
D. Smirnov,J. Leotin,P. Millet,J. Jegoudez,A. Revcolevschi
Physics , 1998, DOI: 10.1016/S0921-4526(98)00633-4
Abstract: Infrared reflectance of alpha'-NaV2O5 single crystals in the frequency range from 50 cm-1 to 10000 cm-1 was studied for a, b and c-polarisations. In addition to phonon modes identification, for the a-polarised spectrum a broad continuum absorption in the range of 1D magnetic excitation energies was found. The strong near-IR absorption band at 0.8 eV shows a strong anisotropy with vanishing intensity in c-polarisation. Activation of new phonons due to the lattice dimerisation were detected below 35K as well as pretransitional structural fluctuations up to 65K.
Study of spin-Peierls transition in alpha'--NaV2O5 by infrared reflectivity
D. Smirnov,P. Millet,J. Leotin,D. Poilblanc,J. Riera,D. Augier,P. Hansen
Physics , 1998, DOI: 10.1103/PhysRevB.57.R11035
Abstract: Polarized infrared reflectivity measurements have been performed on single crystals of the spin-Peierls compound alpha'-NaV2O5 in the temperature range 20-300 K. Pronounced spectral features associated with the formation of the dimerized phase were detected both in the a- and b-polarizations (perpendicular and parallel to the spin-1/2 chains, respectively). The temperature dependence of a salient spectral line at 718 cm^-1 sharply rising below the transition temperature T_SP obeys a (1-T/T_SP)^(2beta) law with T_SP \simeq 34.3$K and beta \simeq 0.25. In addition, a continuum signal is observed in the whole temperature range in the a-polarized optical conductivity spectra. In order to interpret these results, calculations of the static dimerization and of the optical conductivity based on a mean-field and a dynamical treatment of the lattice respectively are proposed.
Quantum Size Effect transition in percolating nanocomposite films
B. Raquet,M. Goiran,N. Negre,J. Leotin B. Aronzon,V. Rylkov,E. Meilikhov
Physics , 2000, DOI: 10.1103/PhysRevB.62.17144
Abstract: We report on unique electronic properties in Fe-SiO2 nanocomposite thin films in the vicinity of the percolation threshold. The electronic transport is dominated by quantum corrections to the metallic conduction of the Infinite Cluster (IC). At low temperature, mesoscopic effects revealed on the conductivity, Hall effect experiments and low frequency electrical noise (random telegraph noise and 1/f noise) strongly support the existence of a temperature-induced Quantum Size Effect (QSE) transition in the metallic conduction path. Below a critical temperature related to the geometrical constriction sizes of the IC, the electronic conductivity is mainly governed by active tunnel conductance across barriers in the metallic network. The high 1/f noise level and the random telegraph noise are consistently explained by random potential modulation of the barriers transmittance due to local Coulomb charges. Our results provide evidence that a lowering of the temperature is somehow equivalent to a decrease of the metal fraction in the vicinity of the percolation limit.
Intersubband magnetophonon resonances in quantum cascade structures
D. Smirnov,O. Drachenko,J. Leotin,H. Page,C. Becker,C. Sirtori,V. Apalkov,T. Chakraborty
Physics , 2001, DOI: 10.1142/S0217979202013274
Abstract: We report on our magnetotransport measurements of GaAs/GaAlAs quantum cascade structures in a magnetic field of up to 62 T. We observe novel quantum oscillations in tunneling current that are periodic in reciprocal magnetic field. We explain these oscillations as intersubband magnetophonon resonance due to electron relaxation by emission of either single optical or acoustic phonons. Our work also provides a non-optical in situ measurement of intersubband separations in quantum cascade structures.
Peculiarities of the transport properties of InMnAs layers, produced by the laser deposition, in strong magnetic fields
V. V. Rylkov,A. S. Lagutin,B. A. Aronzon,V. V. Podolskii,V. P. Lesnikov,M. Goiran,J. Galibert,B. Raquet,J. Leotin
Physics , 2006,
Abstract: Magnetotransport properties of p-InMnAs layers are studied in pulsed magnetic fields up to 30 T. Samples were prepared by the laser deposition and annealed by ruby laser pulses. Well annealed samples show p-type conductivity while they were n-type before the annealing. Surprisingly the anomalous Hall effect resistance in paramagnetic state (T>40 K) and in strong magnetic fields (B > 20 T) appears to be greater than that in ferromagnetic state (T <= 40 K), while the longitudinal resistance rises with the temperature decrease. The negative magnetoresistance saturates in magnetic fields higher then 10T at T near 4 K only, whereas the saturation fields of the anomalous Hall effect resistance are much less (around 2 T at 30K). The total reduction of resistance exceeds 10 times in magnetic fields around of 10T. The obtained results are interpreted on the base of the assumptions of the non-uniform distribution of Mn atoms acting as acceptors, the local ferromagnetic transition and the percolation-like character of the film conductivity, which prevailed under conditions of the strong fluctuations of the exchange interaction. Characteristic scales of the magneto-electric nonuniformity are estimated using analysis of the mesoscopic fluctuations of the non-diagonal components of the magnetoresistivity tensor.
A table-top, repetitive pulsed magnet for nonlinear and ultrafast spectroscopy in high magnetic fields up to 30 T
G. Timothy Noe,Hiroyuki Nojiri,Joseph Lee,Gary L. Woods,Jean Leotin,Junichiro Kono
Physics , 2013, DOI: 10.1063/1.4850675
Abstract: We have developed a mini-coil pulsed magnet system with direct optical access, ideally suited for nonlinear and ultrafast spectroscopy studies of materials in high magnetic fields up to 30 T. The apparatus consists of a small coil in a liquid nitrogen cryostat coupled with a helium flow cryostat to provide sample temperatures down to below 10 K. Direct optical access to the sample is achieved with the use of easily interchangeable windows separated by a short distance of ~135 mm on either side of the coupled cryostats with numerical apertures of 0.20 and 0.03 for measurements employing the Faraday geometry. As a demonstration, we performed time-resolved and time-integrated photoluminescence measurements as well as transmission measurements on InGaAs quantum wells.
New components of the mercury’s perihelion precession  [PDF]
J. J. Smulsky
Natural Science (NS) , 2011, DOI: 10.4236/ns.2011.34034
Abstract: The velocity of perihelion rotation of Mercury's orbit relatively motionless space is computed. It is prove that it coincides with that calculated by the Newtonian interaction of the planets and of the compound model of the Sun’s rotation.
Simple General Purpose Ion Beam Deceleration System Using a Single Electrode Lens  [PDF]
J. Lopes, J. Rocha
World Journal of Engineering and Technology (WJET) , 2015, DOI: 10.4236/wjet.2015.33014
Abstract: Ion beam deceleration properties of a newly developed low-energy ion beam implantation system were studied. The objective of this system was to produce general purpose low-energy (5 to 15 keV) implantations with high current beam of hundreds of μA level, providing the most wide implantation area possible and allowing continuously magnetic scanning of the beam over the sample(s). This paper describes the developed system installed in the high-current ion implanter at the Laboratory of Accelerators and Radiation Technologies of the Nuclear and Technological Cam-pus, Sacavém, Portugal (CTN).
Constraints on velocity anisotropy of spherical systems with separable augmented densities
J. An
Physics , 2011, DOI: 10.1088/0004-637X/736/2/151
Abstract: If the augmented density of a spherical anisotropic system is assumed to be multiplicatively separable to functions of the potential and the radius, the radial function, which can be completely specified by the behavior of the anisotropy parameter alone, also fixes the anisotropic ratios of every higher-order velocity moment. It is inferred from this that the non-negativity of the distribution function necessarily limits the allowed behaviors of the radial function. This restriction is translated into the constraints on the behavior of the anisotropy parameter. We find that not all radial variations of the anisotropy parameter satisfy these constraints and thus that there exist anisotropy profiles that cannot be consistent with any separable augmented density.
On the augmented density of a spherical anisotropic dynamic system
J. An
Physics , 2010, DOI: 10.1111/j.1365-2966.2011.18324.x
Abstract: This paper presents a set of new conditions on the augmented density of a spherical anisotropic system that is necessary for the underlying two-integral phase-space distribution function to be non-negative. In particular, it is shown that the partial derivatives of the Abel transformations of the augmented density must be non-negative. Applied for the separable augmented densities, this recovers the result of van Hese et al. (2011).
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