Читать книгу Quantum Mechanics, Volume 3 - Claude Cohen-Tannoudji - Страница 69

For the sake of simplicity, we shall also start with spinless particles, but including several spin states is fairly straightforward. For bosons, we must use the Bose-Einstein distribution (24) and their average number is therefore:

(55)

We impose periodic boundary conditions in a cubic box of edge length L. The lowest individual energy³ is ek = 0. Consequently, for expression (55) to be meaningful, μ must be negative or zero:

(56)

Two cases are possible, depending on whether the boson system is condensed or not.