The fermion nature of electrons also governs the behavior of electrons in a metal where at low temperatures all the low energy states are filled up to a level called the Fermi energy. The fact that electrons are fermions is foundational to the buildup of the periodic table of the elements since there can be only one electron for each state in an atom (only one electron for each possible set of quantum numbers). The wavefunction which describes a collection of fermions must be antisymmetric with respect to the exchange of identical particles, while the wavefunction for a collection of bosons is symmetric. Fermions include electrons, protons, neutrons. Particles with integer spin are called bosons. HyperPhysics***** Quantum Physics ***** Particlesįermions are particles which have half-integer spin and therefore are constrained by the Pauli exclusion principle. You can't just take a pile of identical fermions and put them all at the same place the laws of quantum mechanics won't allow it." The fact that two identical fermions can't occupy the same state is further described by the Pauli exclusion principle, and the fact that bosons can is further described as Bose-Einstein condensation.Ĭarroll, "The Particle at the End.", Ch 2 The difference between the two is that fermions take up space, while bosons can pile on top of one another. Particles of integer spin obey Bose-Einstein statistics, whereas those of half-integer spin behave according to Fermi-Dirac statistics.Ĭarroll describes fermions and bosons as follows: "Particles come in two types: the particles that make up matter, known as 'fermions', and the particles that carry forces, known as 'bosons'. The spin classification of particles determines the nature of the energy distribution in a collection of the particles. Exceptions are the graviton with spin 2 and the Higgs boson with spin 0. The photon is a boson with spin 1, which is a typical boson spin. The quarks are also fermions with spin 1/2. The electron is a fermion with electron spin 1/2. Half-integer spin fermions are constrained by the Pauli exclusion principle whereas integer spin bosons are not. One essential parameter for classification of particles is their "spin" or intrinsic angular momentum. Spin classification of particles Spin Classification
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