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FERMI GLASS - P

The Fermi Glass: Theory and Experiment - PHILIP W. ANDERSON ... readable

theory

pdf 1977 - Freedman-Hertz - the theory of Fermi glass

We have constructed a theory to account for the effects of the electron-electron interaction on the
low-temperature (T «Tz) electronic properties ot' disordered solids. Although we have placed special emphasis on the case where the single-particle states at the Fermi energy are localized, the theory we have constructed is easily adapted to the
case of extended states. The low-lying excitations of the system are viewed as quasiparticles. Each quasiparticle is then viewed as a single entity moving in the self-consistent field of all the other quasiparticles. The resulting theory has the form
of a mean-field theory for the quasiparticles.

We have shown that the low-temperature electronic contribution to the specific heat is unaffected by interactions

Landau about quasiparticles

Although the originators of the various quasiparticles pursued somewhat different approaches, they all shared the same attitude to the basic problem of freedom. Perhaps the central challenge for condensed-matter physicists at the time was to conceptualize the state of freedom of particles in densely packed bodies. Electrons in metals, for example, were treated as free particles in band theories of conductivity. In theories of ferromagnetism, however, the same electrons were usually assumed to be bound to particular atoms. Similar dilemmas arose in practically every major area in the field. Landau – as well as Frenkel, Bohm and a few others – saw both free and bound approximations as far too crude.

They searched instead for more complex mathematical models of freedom along “collectivist” lines, whereby particles would be
sufficiently free but not entirely independent of each other. The various solutions they found now usually come under the general heading of “quasiparticles” and have since become the central concept of the collectivist approach in many-body physics. It is not entirely coincidental that most of the physicists who introduced such notions and methods into physics viewed collectivism in a positive light and sympathized with various versions of socialist ideas.

experiment

The main point is to show that in a number of disordered metals with saturated or nearly saturated resistivity no reduction of N(0) is observed compared to the value of N(0) in the ordered state. In other words, while some metals show N (0) decrease upon disordering, others have N (0) increased or unchanged; however, all of them show typical saturation behavior. If this is the case, relation (2) is not universal, and the exchange theory of Ref. 1 is not a common cause of saturation in various metals. Yet a good deal of evidence suggests that resistivity saturation is a universal effect manifesting itself in all metals with sufficiently short electronic mean free path

https://en.wikipedia.org/wiki/Exchange_interaction