Fermi Gas

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Fermi gas

[′fer·mē ‚gas]
(statistical mechanics)
An assembly of independent particles that obey Fermi-Dirac statistics, and therefore obey the Pauli exclusion principle; this concept is used in the free-electron theory of metals and in one model of the behavior of the nucleons in a nucleus. Also known as Fermi-Dirac gas.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Fermi Gas


a gas that consists of particles with half-integral spin and obeys Fermi-Dirac statistics. Fermi gas that consists of noninteracting particles is called ideal Fermi gas. Fermi gases include electrons in metals and semiconductors, electrons in atoms with large atomic numbers, nucleons in heavy atomic nuclei, and gases consisting of quasiparticles with half-integral spin.

At a temperature T = 0°K, an ideal Fermi gas is in the ground state, and the particles of the gas occupy all quantum states with energy up to a certain maximum value, which depends on the gas density and is called the Fermi level (EF). Quantum states with energy E > EF are empty; such a distribution of occupied and empty states corresponds to complete degeneracy of the Fermi gas. At T ≠ 0°K, the mean occupation number for a quantum state of an ideal Fermi gas is described by the Fermi-Dirac distribution function.

A Fermi level also exists for a nonideal Fermi gas, although the particles of such a gas do not occupy specific quantum states. In a nonideal Fermi gas consisting of electrons in a metal, the formation of pairs of correlated electrons (the Cooper effect) and the transition of the metal to the superconducting state may occur at very low temperatures because of the attraction of electrons with equal but oppositely directed momenta and spins. A Fermi gas consisting of electrons in heavy atoms is described by the Thomas-Fermi model (seeSELF-CONSISTENT FIELD).


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The Fermi gas model of the nucleus assumes that the nucleons are free to move inside the potential well of the nucleus.
Lee, "Polylogarithmic analysis of chemical potential and fluctuations in a D-dimensional free Fermi gas at low temperatures," Journal of Mathematical Physics, vol.
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The gas of quasi-particles, which are associated with operators (20), can also be used to compute the thermodynamic variables for a degenerate Fermi gas (as an alternative to the Sommerfeld expansion).
The discovery of the quantum statistics that incorporate Pauli's exclusion principle [1], made independently by Fermi [2] and Dirac [3], allowed the qualitative understanding of several physical phenomena--in a wide range of values of the particle density, from astrophysical scales to subnuclear ones--in terms of the ideal Fermi gas (IFG).
with the occupation probability of a free Fermi gas with a Fermi momentum [k.sub.F]:
That was the first glimpse of a new state of matter--a kind of ultrafrigid vapor--with the ponderous label "strongly interacting, degenerate Fermi gas." Named after the Italian-born physicist Enrico Fermi, these aggregations of particles can behave, according to quantum mechanics, as if they're a single entity.
Fifteen additional contributions follow discussing parity mixing, superconductivity, quantum spin-orbit correlation in crystals, Dirac fermions in cuprates and graphenes, magnetism of iron pnictides, liquid crystals, bilayer quantum Hall systems, bird flocking as an example of self-organization, pairing behavior in the unitary Fermi gas, crackling noise, growing length scales, dynamics of semiconductor nanocrystals, polycrystal plasticity, molecular beam epitaxy, and dislocation theory.