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The Fermi energy is a concept in quantum mechanics usually referring to the energy difference between the highest and lowest occupied single-particle states in a quantum system of non-interacting fermions at absolute zero temperature. In a Fermi gas the lowest occupied state is taken to have zero kinetic energy, whereas in a metal the lowest occupied state is typically taken to mean the bottom of the conduction band. Confusingly, the term "Fermi energy" is often used to refer to a different but closely related concept, the Fermi ''level'' (also called electrochemical potential).〔The use of the term "Fermi energy" as synonymous with Fermi level (a.k.a. electrochemical potential) is widespread in semiconductor physics. For example: (''Electronics (fundamentals And Applications)'' ) by D. Chattopadhyay, (''Semiconductor Physics and Applications'' ) by Balkanski and Wallis.〕 There are a few key differences between the Fermi level and Fermi energy, at least as they are used in this article: * The Fermi energy is only defined at absolute zero, while the Fermi level is defined for any temperature. * The Fermi energy is an energy ''difference'' (usually corresponding to a kinetic energy), whereas the Fermi level is a total energy level including kinetic energy and potential energy. * The Fermi energy can only be defined for non-interacting fermions (where the potential energy or band edge is a static, well defined quantity), whereas the Fermi level (the electrochemical potential of an electron) remains well defined even in complex interacting systems, at thermodynamic equilibrium. Since the Fermi level in a metal at absolute zero is the energy of the highest occupied single particle state, then the Fermi energy in a metal is the energy difference between the Fermi level and lowest occupied single-particle state, at zero-temperature. ==Introduction== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fermi energy」の詳細全文を読む スポンサード リンク
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