Abstract
Quasiparticles and collective effects may have seemed exotic when first proposed in the 1930s, but their status has blossomed with their confirmation by today's sophisticated experiment techniques. Evidence has accumulated about the interactions of, say, magnons and rotons and with each other and also other quasiparticles (QPs). We briefly review the conjectures of their existence necessary to provide quantitative agreement with experiment which in the early period was their only reason for existence. Phase transitions in the Anderson model, the Kondo effect, rotonβroton interactions, and highly correlated systems such as heliumβ4, the quantum Hall effect, and BoseβEinstein condensates are discussed. Some insulator and superconductor theories seem to suggest that collective interactions of several QPs may be necessary to explain the behavior. We conclude with brief discussions of the possibility of using the GrΓΌneisen parameter to detect quantum critical points and some background on bound states emerging from the continuum. Finally, we present a summary and conclusions and also discuss possible future directions. Β© 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012