Spectral weight

In this contribution we will deal with electron-electron correlation in solids and how to learn about these by means of inelastic X-ray scattering both in the regime of small and large momentum transfer. We will compare the predictions of simple models (free electron gas, jellium model) and more sophisticated ones (calculations using the self-energy influenced spectral weight function) to experimental results. In a last step, lattice effects will be included in the theoretical treatment. 

Spectra-temporal weighting was found to be important only in quality judgements on speech codecs. Probably in music all spectra-temporal components in the signal, even silences, carry information, whereas for speech some spectra-temporal components, like formants, clearly carry more information then others, like silences. Because speech databases used in this paper are all telephone-band limited spectral weighting turned out to be only of minor importance and only the weighting over time had to be modelled. 

Erwood and Xydeas, 1990] Erwood, A. and Xydeas, C. (1990). A multiframe spectral weighting system for the enhancement of speech signals corrupted by acoustic noise. In SIGNAL PROCESSING V Theories and Applications, pages 1107-1110. Elsevier. 

Finally, we introduce the important combination of retarded and advanced functions known as spectral or spectral weight function... 

In this case, the fact that a large resonant enhancement is seen of the states at around 1 eV is consistent with the behaviour of other dominantly trivalent Ce-based systems, as it is here that the 4f° photoemission final-state spectral weight occurs for systems with a 4f1 initial-state configuration. Thus, from the resonant photoemission data, we can confirm the trivalent nature of the Ce ions in Ce2 C72 and conclude that there is relatively weak hybridisation between the Ce 5d and the C 2s/2p states of the fullerene cage in this case. A shorthand notation for the cerium dimetallofullerene could thus be (Ce2)6+(C72)6. ... 

Neale, P.J., and Kieber, D.J. (2000) Assessing biological and chemical effects of UV in the marine environment spectral weighting functions. In Causes and Environmental Implications of Increased UV-B Radiation (Hester, R.E., and Harrison, R.M., eds.), pp. 61-83, The Royal Society of Chemistry, Cambridge, UK. 

Figure 13 Relative weight of the 0/Ag(2 1 0) energy loss intensities plotted vs. the angle of incidence and parametric in Ex. While at low E the spectral weight is isotropic, at high E the population of the site associated to the 56 meV mode is favoured when the O2 molecules impinge normally to the (10 0) nanofacets. Two exposures are reported for the lowest impact energy to show that the relative weight of the 56 meV peak increases with coverage.

Keywords High Tc superconductors, infrared conductivity, spectral weight... 

From the optical conductivity, we compute the spectral weight or partial sum rule defined in Eq.l. We show in Fig3-a and -b the temperature variation... 

Figure 3. Partial sum rule shown for underdoped (a) and (b), and overdoped (c) samples, for selected cutoff frequencies. Full symbols represent the spectral weight, integrated from 0+, hence without the superfluid contribution. Open symbols include (below Tc) the superfluid weight. Fig3-b and -c represent the intraband spectral weight, hence —Ek, as a function of temperature. The dotted lines are 12 best fits to the normal state data.

We have measured with great accuracy the reflectivity of electron doped Pr2 sCe, Cu() at various Ce doping levels. An optical conductivity spectral weight analysis shows that a partial gap opens at low temperatures for Ce concentrations up to x = 0.15. A spin density wave model reproduces satisfactorily the data. 

A simple physical picture that is consistent with the above results is that above T one has coherent itinerant quasiparticle behavior over the entire Fermi surface, observed as an anomalous Fermi liquid. Below T one loses that coherent behavior for a portion of the Fermi surface near the antinodes the hot quasiparticles (those whose spin-fluctuation-induced interaction is strongest) found there enter the pseudogap state its formation is characterized by a transfer of quasiparticle spectral weight from low to high frequencies that produces the decrease in the uniform spin susceptibility below T. The remainder of the Fermi surface is largely unaffected. 

The transfer of spectral weight from low frequencies to high frequencies that accompanies the formation of pseudogap matter is the inverse of process in heavy electron materials by which at some onset temperature the itinerant coherent heavy electron state emerges out of the local moments that make up the Kondo lattice. It has recently proved possible to develop a two-fluid description that describes this emergent... 

Figure 2. Band-fits for the conducting band of LSCO of [6], corresponding to the Fermi surfaces of Fig. 1, illustrating the spectral weight transfer from the lower (oxygen) band to the resonant band upon doping...

Figure 2. The spectral weight of the lower Hubbard (copper) band (-1 < 5 < 0) and the singlet-correlated (copper-oxygen) band (0 < S < 1). Note, the optimal doping corresponds to the half-filled copper-oxygen band which is reached for S = 1 /3.

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