Fermi surface spanning

Electron-diffraction studies revealed that these phenomena are coupled with the occurrence of superstructures which are caused by charge-density waves. Theoretical work suggests that these two-dimensional compounds are likely to be susceptible to Fermi-surface-driven instabilities. The two-dimensional character of the Fermi surface implies planar surfaces normal to the layers. Large parallel sections of Fermi surface, spanned by a vector qo, lead, in real-space potential, to an oscillatory component of wavelength 1/qo- This must introduce a periodic... 

Fig. 6.5 Scattering between filled and empty states near the Fermi surface. For the Fermi sphere of a free-electron gas the maximum number of such events occurs for q = 2kf. For a Fermi surface with flat regions the number of such events is dramatically enhanced for q = Q, the spanning wave vector.

The resulting fit parameters are listed in Table 11.7 for each of the blends and for pure PAni. The value of Tm represents the energy of phonons with wavevector spanning the Fermi surface of highly anisotropic metals it is about 1400 K in polyacetylene [104], but higher values give a slightly better fit for the PAni case. Since is not determined accurately by the data, a value of 2000 K for all samples were taken. 

The spectral features in the data shown in Figures 172 and 173 resemble those expected for a density-wave state, for example, as in (TMTSF)2PF6 where an SDW gap is formed at around 100 cm" in the direction perpendicular to the chains [1212]. With this interpretation, the resonance at 70 cm Vould be identified with the pinned collective mode. The spectral weight within the 70 cm resonance corresponds to a small fraction (approximately 10%) of the oscillator strength, which was redistributed from below 2A to above 2A. Alternatively, since the gap spans only a part of the Fermi surface, the results reported here can be interpreted in the context of the correlation-induced semimetallic state proposed by Vescoli et al. [1213]. 

There are no direct Fermi surface studies of the transition metal Laves phases -which is unfortunate in light of the part they have played, and continue to play, in our understanding of f electron behavior. The Np Laves phases have played a special role because they appear to span the critical separation between localized and itinerant behavior (Aldred et al. 1974). The U and Ce transition metal Laves phases occur on the itinerant side of the Hill (1970) plots, but some do approach, and just cross, the critical separation. The transition to magnetic behavior can be very closely approached by considering NpRu Osz-x alloys (Aldred et al. 1975). Because their properties are consistent with the Hill correlation, it would initially appear that one has a nice simple picture based on a direct f-f overlap analysis. Certainly, a Hill plot analysis was part of the motivation for the extensive studies of the Np materials. However, it appears that these materials heavily involve interaction with the ligands. 

The work function (<[>) is defined as the energy difference between the Fermi level (Ef) and the vacuum level above a sample (Evac).It is known that < > of metals depends on the crystal face exposed to vacuum [1-3], e.g., ( > spans a range of 0.5 eV for copper (100), (110), and (111) surfaces [1,2], As EF is constant, this observation has been explained by crystal face dependent intrinsic surface dipoles . Differences in the geometric and, consequently, electronic structure cause a different amount of the electronic cloud to spill out of the bulk into the vacuum [3,4], The resulting dipoles change Evao and thus impact <]>. 

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