15 - Ideal Fermi gas

Summary

Why is it that particles with half-integer spin are Fermi particles whereas particles with integer spin are Bose particles? An explanation has been worked out by Pauli from complicated arguments from quantum field theory and relativity. He has shown that the two must necessarily go together … but we have not been able to reproduce his arguments on an elementary level. This probably means we do not have a complete understanding of the fundamental principle involved…

R. P. Feynman, R.B. Leighton and M. Sands, Feynman Lectures on Physics, Volume 3, Chapter 4, Section 1, Addison-Wesley, Reading, MA (1963)

Introduction

Particles with half-integer angular momentum obey the Pauli exclusion principle (PEP) – a restriction that a non-degenerate single-particle quantum state can have occupation number of only 0 or 1. This restriction was announced by W. Pauli in 1924 for which, in 1945, he received the Nobel Prize in Physics. Soon after Pauli, the exclusion principle was generalized by P. Dirac and E. Fermi who – independently – integrated it into quantum mechanics. As a consequence half-integer spin particles are called Fermi–Dirac particles or fermions. PEP applies to electrons, protons, neutrons, neutrinos, quarks – and their antiparticles – as well as composite fermions such as He³ atoms. Thermodynamic properties of metals and semiconductors are largely determined by electron (fermion) behavior.