Order parameter and Bose-Einstein condensation

I want to study about order parameter and symmetry breaking related to bose einstein condensation in interacted system. Which book i should read? also i want to learn this in second quantization notation.

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I mean the two main textbooks for this are:

• Pethic & Smith, Bose Einstein condensation in dilute gases

• Stringary & Pitaevski, Bose Einstein condensation (and Superfluidity)

which cover both the theory and the experimental stuff.

Otherwise, any lecture notes online cover the basics of BEC.

• The order parameter is usually chosen as the population in the ground state $$|\Psi_0|^2$$ which is $$\sim 0$$ for $$T>T_c$$ and $$\underbrace{\neq}_{\text{macroscopically}} 0$$ for $$T and $$1$$ at $$T=0$$.
• The symmetry broken is $$U(1)$$, since the BEC is a single mega-wavefunction with just one phase. The choice of a single phase breaks the $$U(1)$$ (the group of phase factors) symmetry of the thermal state.