I am currently following a course of condensed matter physics and quite enjoying it. But after doig some research I found that many book deal with QFT applied to condensed matter. I wonder what all the calculus of QFT is needed to describe those phenomenas. I kinda feel that relativistic description given by QFT is inevitable but things like propagators, Feynman Diagrams and renomalization... So if someone could explain me what this necessity or council one introduction to the subject. Thanks a lot.