what is fermi energy

The Fermi energy is a concept in quantum mechanics that refers 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. It is named after physicist Enrico Fermi and is an important quantity in the physics of quantum liquids, solid-state physics of metals and superconductors, as well as in nuclear physics and understanding the stability of white dwarf stars against gravitational collapse. 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. The Fermi energy is also closely related to the Fermi level, which is the top of the collection of electron energy levels at absolute zero temperature. The Fermi energy is used to determine the electrical and thermal characteristics of solids and is an important concept in superconductor physics and quantum mechanics.