Over the last few years, we have studied the phenomenon of superconductivity from a chemist's point of view. Starting from the special chemical bonding picture of some rare earth carbides and carbide halides, a general viewpoint on the origin of superconductivity was proposed [1]. This so-called "flat band steep band" scenario is based on the chemical origin of pairwise attractive interaction between conduction electrons. The flat bands provide a vanishing Fermi velocity for some conduction electrons in the normal conducting state. Provided these electrons get spin-paired the scenario of Bose condensation as described by London is met [2]. The "steep band" provides a mobile electronic reservoir and suppresses the instability of a structure. This view is formally similar to a physical model based on the interplay of itinerant electrons in a wide band with local pairs of electrons in a narrow band [3]. However, in extracting the flat hand/steep band features from calculated band structures we address the specific chemical bonding in actual superconductors.
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