Quasiparticles and collective excitations

There is another notion which is also very important for the description of the properties of solids, that of collective excitations . In contrast to quasiparticles, these are bosons, they bear no resemblance to constituent particles of a real system, and they involve collective (that is, coherent) motion of many physical particles. We summarize here the most common quasiparticles and collective excitations encountered in solids  

In the following chapters we will explore in detail the properties of the some of 

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In chapter 2 we provided the justification for the single-particle picture of electrons in solids. We saw that the proper interpretation of single particles involves the notion of quasiparticles these are fermions which resemble real electrons, but are not identical to them since they also embody the effects of the presence of all other electrons, as in the exchange-correlation hole. Here we begin to develop the quantitative description of the properties of solids in terms of quasiparticles and collective excitations for the case of a perfectly periodic solid, i.e., an ideal crystal. 

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