Fermi surface measurements

First direct Fermi surface measurements (de Haas-van ... 

The Fermi surfaces of these salts have been studied by measuring the quantum oscillations [183] such as SdH (Shubnikov-de Haas) and dHvA and geometrical oscillations (AMRO, angle-dependent magnetoresistance oscillation) ([4], Appendix, pp 445 48). The Fermi surface of k-(ET)2Cu(NCS)2 (Fig. 14c) calculated based on the crystal structure is in good agreement with those observed data [225]. 

An early success of quantum mechanics was the explanation by Wilson (1931a, b) of the reason for the sharp distinction between metals and non-metals. In crystalline materials the energies of the electron states lie in bands a non-metal is a material in which all bands are full or empty, while in a metal one or more bands are only partly full. This distinction has stood the test of time the Fermi energy of a metal, separating occupied from unoccupied states, and the Fermi surface separating them in k-space are not only features of a simple model in which electrons do not interact with one another, but have proved to be physical quantities that can be measured. Any metal-insulator transition in a crystalline material, at any rate at zero temperature, must be a transition from a situation in which bands overlap to a situation when they do not Band-crossing metal-insulator transitions, such as that of barium under pressure, are described in this book. 

Thus, measurements of k and Cp provided first hints for possible nodes in the energy gap. More detailed investigations, however, point to different scenarios, in particular those based on Fermi-surface nesting. Also there are discrepancies between experimental data and the (s + g)-wave description. 

In the atomic context the need for relativistic corrections to Exc[n] is obvious and has led to the development of the relativistic LDA (RLDA) [5,6,24]. On the basis of RLDA calculations for metallic Au and Pt, MacDonald et al. [25,26] have concluded that in solids relativistic contributions to Exc[n] can produce small but significant modifications of measurable quantities, as eg. the Fermi surface area. On the other hand, it has been shown [7] that the RLDA suffers from several shortcomings, eg. from a drastic overestimation of transverse exchange contributions, thus making the RLDA a less reliable tool than its nonrelativistic counterpart. As relativistic corrections are clearly misrepresented by the RLDA, it seems worthwhile to reinvestigate the role of relativistic arc-effects in solids on the basis of a more accurate form for Exc[n. ... 

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