The coherent dynamic structure factor $(Q, co) of liquid Cs has been measured by inelastic neutron scattering near the melting point at 308 K. Using triple-axis spectrometers at the Institut Laue-Langevin in Grenoble and at the Forschungs-Reaktor Munchen the scattering law was determined for energy transfers %co from -2 to 10 meV and for momentum transfers AQ between 0.2 and 2.55 A . The measurement has been corrected for all significant effects, including multiple and incoherent scattering as well as resolution broadening. In this paper we present mainly experimental results including a table of the measured scattering law. The analysis of the dispersion relation and the full width at half maximum of the longitudinal current correlation function J,(Q,co) reveals an anomalous dispersion due to shear relaxation in the liquid. In the vicinity of the structure-factor maximum the measured half-width of the coherent central peak of $(Q, co) confirms recent theoretical assumptions of a collective-diffusion-like structural relaxation process in dense liquids near the melting point. PACS number(s): 62.15.+i, 67.40.Fd
The static structure factor, S(Q), of liquid rubidium has been studied by neutron diffraction for temperatures up to 2000 K and pressures up to 139 bar near saturation conditions, corresponding to an expansion of the liquid from 1.46 to 0.54 gcm-3. The characteristic changes of the scattering behaviour and of the microscopic structure approaching the M-NM transition region are discussed. A comparison of these results with simple hard sphere model calculations is given.
The paper presents the first neutron scattering investigation of the static structure factor S(Q) of expanded liquid cesium from the melting point up to its critical point at conditions near the liquid‐vapour coexistence curve (critical data of cesium: Tc = 1924 K, pc = 92.5 bar, dc = 0. 379 g/cm3). The characteristic changes of the microscopic structure — such as the distance and number of nearest neighbours — are derived as a function of density. The reported results give useful information about the density dependent changes in the electronic structure in course of the transition from a metallic to a nonmetallic state which occurs in the expanded metal. In particular, the results provide direct experimental evidence for the limitation of the nearly‐free‐electron (NFE) model in describing the electrical transport properties of low density fluid cesium.
Raman scattering experiments have been performed on single-crystal samples of YBa2Cu307 in order to investigate superconducting gap excitations. The electronic contribution to the total scattering intensity can be fitted well by a theoretical model of light scattering from quasiparticle pairs. Depending on the measuring symmetry, mean gap energies are found ranging from 3.0 to 5.5 kgTc The discovery of the new high-T, superconductors' has initiated unprecedented experimental and theoretical efforts in trying to understand the coupling mechanism. ' While pair correlations of charge carriers seems to follow from the observed quantum of flux (@n h/2e) and from Andreev scattering, experiments on the determination of the energy gap, 2h, still disagree widely. 6 may show considerable anisotropy, as was suggested from the beginning by both the structural and the superconducting properties of YBa2Cu307. A recent tunneling study on single crystals reported gap values of 3.6 and 5.9 ktt T, for wave vectors parallel and perpendicular to the CuO a bplanes-, respectively. As was shown first b Dierker, Klein, Webb, and Fisk in the 815 compounds, Raman scattering may
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