# Rigorous distinction between quasiparticles and collective excitations

I would like to hear your opinion on the question whether there is an accepted distinction between both concepts in condensed matter physics. I would tend to use the word quasiparticle for dressed fermionic particles and the term collective excitation in the case of bosonic excitation. But considering for example magnons in ferromagnets makes it very arbitrary kind of definition since magnons can be viewed (if I am not wrong) both as quasiparticles and also as collective excitations.

• In nuclear physics, we have collective excitations such as rotations and vibrations, and quasiparticle excitations of the nucleons. There is no clean distinction between the two. For example, one can have a chain of even-even nuclei with neutron and proton numbers $(N,Z)$, $(N,Z+2)$, $(N,Z+4)$, ... such that one end of the chain demonstrates nearly pure quasiparticle excitations, while the other end is a deformed rotor with highly collective excited states. The ones in between interpolate between these two extremes. – Ben Crowell Sep 12 '14 at 15:45