Composite particles (such as
hadrons, nuclei, and atoms) can be bosons or fermions depending on their constituents. More precisely, because of the relation between spin and statistics, a particle containing an odd number of fermions is itself a fermion. It will have a half-integer spin. The number of bosons within a composite particle made up of simple particles bound with a potential has no effect on whether it is a boson or a fermion. Examples include the following: • A baryon, such as the proton or neutron, contains three fermionic quarks. • The nucleus of a
carbon-13 atom contains six protons and seven neutrons. • The atom
helium-3 (3He) consists of two protons, one neutron, and two electrons. The
deuterium atom consists of one proton, one neutron, and one electron. The fermionic or bosonic behaviour of a composite particle is only observed when the constituent particles remain far apart. When they are close together, the spatial structure becomes important and the composite particles behave according to their constituent makeup. Fermions can exhibit bosonic behavior when they become bound in pairs. This is the origin of
superconductivity and the
superfluidity of helium-3. In superconducting materials, electrons interact through the exchange of
phonons, forming
Cooper pairs, while in helium-3, the atoms interact and pair via spin fluctuations. The quasiparticles of the
fractional quantum Hall effect are also known as
composite fermions; they consist of electrons with an even number of quantized vortices attached to them. ==See also==