The Variety of Finite Fermion Systems and Their Basic Properties

Abstract

Many-fermion systems are all around us. Any form of massive matter is a discrete assembly of atoms, each of them constituted of a dense nucleus surrounded by a diffuse electron cloud. Nuclei themselves are built from interacting neutrons and protons, which are ultimately small compounds of quarks. Electrons, neutrons, protons, and quarks are fermions. Atoms themselves may also be fermions, if their total spin, built from those of electrons, neutrons, and protons, is half-integer (in units of ħ), otherwise they are bosons. There are a few other bosonic particles in nature, especially the particles mediating elementary interactions but, apart from exceptions, most assemblies of massive particles are built from fermions.