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G. Chaboussant M.-H. Julien Y. Fagot-Revurat M. Hanson L.P. Lévy C. Berthier M. Horvatic O. Piovesana 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):167-181
In a magnetic field, spin-ladders undergo two zero-temperature phase transitions at the critical fields Hc1 and Hc2. An experimental review of static and dynamical properties of spin-ladders close to these critical points is presented. The
scaling functions, universal to all quantum critical points in one-dimension, are extracted from (a) the thermodynamic quantities
(magnetization) and (b) the dynamical functions (NMR relaxation). A simple mapping of strongly coupled spin ladders in a magnetic
field on the exactly solvable XXZ model enables to make detailed fits and gives an overall understanding of a broad class of quantum magnets in their gapless
phase (between Hc1 and Hc2). In this phase, the low temperature divergence of the NMR relaxation demonstrates its Luttinger liquid nature as well as
the novel quantum critical regime at higher temperature. The general behavior close these quantum critical points can be tied
to known models of quantum magnetism.
Received: 13 March 1998 / Received in final form and Accepted: 21 July 1998 相似文献
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Sebastian Groh Carmen C. GarciaAyrat Murtazin Vlasta Horvatic Kay Niemax 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009
Monodisperse droplets from aqueous analyte solutions with selected diameters in the range 35–67 µm are introduced into an inductively coupled plasma with frequencies between 1 to 10 droplets per second. The effect of desolvation and atomization in the ICP is studied end-on by optical emission spectroscopy employing simultaneously up to three calibrated monochromators with fast photomultipliers. The onsets of desolvation and analyte atomization and the extremely fast diffusion of hydrogen in the ICP and its effect on the plasma are studied by simultaneous measurements of hydrogen, analyte and Ar lines. The local cooling by analyte atomization as well as the recovering of the plasma excitation temperature after completed atomization is measured quantitatively in dependence on time applying the Boltzmann plot method to simultaneously recorded line intensities of atomized analyte atoms which act as plasma probes. Furthermore, it is shown that relatively small differences in analyte mass cause significant temperature changes during atomization and, as consequence, strong variations of the emission intensity of analyte lines during atomization if measured by end-on observation. 相似文献
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C. Vadla K. Niemax V. Horvatic 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(2):139-147
The energy-pooling rate coefficient for the
process has been measured. The barium atoms were excited by a cw diode laser tuned to the frequency of the 791.3 nm intercombination
line and the metastable atoms in the 6s5d state were produced due to radiative and collisional depopulation of the laser-excited 6s6p state. The measurements were performed at number densities of about and at 30 mbar argon as the buffer gas. Most of the barium ground state atoms in the excitation zone were transferred to
the trip let metastable state at the laser pump power applied. The energy pooling rate coefficient was determined by comparing
the fluorescence intensity of the barium 553.6 nm resonance line and the fluorescence intensity of the intercombination line
791.3 nm. In addition, the populations of the metastable atoms were probed with low intensity laser radiation from a single
mode ring dye laser. The rate coefficient was found to be at .
Received: 11 April 1997 / Revised: 24 September 1997 / Accepted: 10 December 1997 相似文献
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Julien M Feher T Horvatic M Berthier C Bakharev ON Segransan P Collin G Marucco J 《Physical review letters》2000,84(15):3422-3425
Doping the high- T(c) superconductor YBa2Cu3O6.7 with 1.5% of nonmagnetic Zn impurities in CuO2 planes is shown to produce a considerable broadening of 63Cu NMR spectra, as well as an increase of low-energy magnetic fluctuations detected in 63Cu spin-lattice relaxation measurements. A model-independent analysis demonstrates that these effects are due to the development of staggered magnetic moments on many Cu sites around each Zn and that the Zn-induced moment in the bulk susceptibility might be explained by this staggered magnetization. Several implications of these enhanced antiferromagnetic correlations are discussed. 相似文献
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Vlasta Horvatic Damir Veza Kay Niemax Cedomil Vadla 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008
A simple and accurate way of determining atom number densities in dense rubidium vapors is presented. The method relies on the experimental finding that the reduced absorption coefficients of the Rb triplet satellite bands between 740 nm and 750 nm and the triplet diffuse band between 600 nm and 610 nm are not temperature dependent in the range between 600 K and 800 K. Therefore, the absolute values of the reduced absorption coefficients of these molecular bands can provide accurate information about atomic number density of the vapor. The rubidium absorption spectrum was measured by spatially resolved white-light absorption in overheated rubidium vapor generated in a heat pipe oven. The absolute values for the reduced absorption coefficients of the triplet bands were determined at lower vapor densities, by using an accurate expression for the reduced absorption coefficient in the quasistatic wing of the Rb D1 line, and measured triplet satellite bands to the resonance wing optical depth ratio. These triplet satellite band data were used to calibrate in absolute scale the reduced absorption coefficients of the triplet diffuse band at higher temperatures. The obtained values for the reduced absorption coefficient of these Rb molecular features can be used for accurate determination of rubidium atomic number densities in the range from about 5 × 1016 cm− 3 to 1 × 1018 cm− 3. 相似文献
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C. Vadla K. Niemax V. Horvatic R. Beuc 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,34(3):171-184
Excitation transfer between the barium low lying excited states 6s6p 3 P 1 0 , 6s5d 1 D 2 and 6s5d 3 D J by collisions with He,Ar,Xe and Ba has been investigated. The population densities in all levels involved were probed by absorption or by fluorescence usingcw lasers. The depopulation cross sections of the Ba3 P 1 0 state by collisions with noble gases were found to be σHe(3 P 1 0 )=5.5·10?16 cm2, σAr(3 P 1 0 )=4.6·10?16 cm2, and σXe(3 P 1 0 )=1.7·10?16 cm2. For Ar, the collisional depopulation of the3 P 1 0 level is exclusively due to the transition to the1 D 2 state. Under the assumption that the3 D J metastable states are populated collisionally by1 D 2 →3 D J transfer only, we have deduced the upper limit for the corresponding cross section σ 13 Ar =1.5·10?18 cm2. From the Ba1 D 2 and Ba3 D J steady-state diffusion distributions, collisional relaxation rates of the1 D 2 and3 D J levels were evaluated. The collisional relaxation rates by Ar and Ba yielded total cross sections for the depopulation of metastable levels: σAr(1 D 2)=1.5·10?17 cm2, σBa(1 D 2)?1·10?13 cm2, σAr(3 D J)=7·10?21 cm2, and σBa(3 D J)=1·10?15 cm2. Furthermore, it was found that the main contribution of the collisional depopulation of the1 D 2 state by Ar is related to back transfer to the3 P J 0 state, whereas the deactivation of the3 D J metastable state is due to back transfer to the1 D 2 state. Taking into account other cross sections reported in literature we can conclude that collisional deactivation of both metastable levels by Ba ground state atoms can be attributed to their mutual collisional mixing. 相似文献