Pseudogaps and Photoemission Experiments
The study of the density of states (DOS) of a material is important to understand its properties, particularly regarding its metallic or insulating character. If a gap exists at the Fermi energy E F, then the system is insulating. However, if at that Fermi energy the DOS is nonzero and featureless, the system should be metallic (unless Anderson localization is at work). In many transition-metal oxides, such as the-high temperature superconductors and the manganites, evidence is accumulating that a “pseudogap” exists at E F. A pseudogap is an intermediate case between a fully established gap, and a standard metallic case with no gap. The DOS of a pseudogapped system has a substantially depleted DOS at E F, but its actual value does not reach exactly zero. The explanation of pseudogap behavior has been at the forefront of investigations in cuprates [18.1], and a similar concept is rapidly reaching similar relevance in manganites. In fact, a pseudogap has already been observed in theoretical investigations of models for Mn oxides, as well as in photoemission experiments in bilayer manganites. Both issues are reviewed in this chapter. Clearly, this is a fairly novel subarea of investigations in manganites, and the research is at its early stages. Considerable work should be devoted to the study of this phenomenon in Mn oxides and related compounds.
KeywordsFermi Energy Spectral Weight Anderson Localization Incoming Photon Photoemission Experiment
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