11. Fluctuations in a Fermi gas. Show for a single orbital of a fermion system that <(AN)?) = (1 – (N>), (91) if (N) is the average number of fermions in that orbital. Notice that the fluctuation vanishes for orbitals with energies deep enough below the Fermi energy so that (N) = 1. By definition, AN = N – (N). -

11. Fluctuations in a Fermi gas. Show for a single orbital of a fermion system that <(AN)?) = (1 – (N>), (91) if (N) is the average number of fermions in that orbital. Notice that the fluctuation vanishes for orbitals with energies deep enough below the Fermi energy so that (N) = 1. By definition, AN = N – (N). -