New interpretation of the quasiparticle weight Z(Q) for superfluid 4He

Glyde and Griffin have recently given a new interpretation of the quasiparticle dispersion relation for superfluid 4He. The low Q phonon peak in S(ovrarr|Q,ω) corresponds to a zero sound mode while the high Q maxon-roton peak is a strongly-renormalized single particle excitation. We propose that Z(Q) should be viewed as the superposition of the weights of zero sound and maxon-roton excitations. We also speculate that the ratio Z(maxon)/Z(roton) may reflect the value of the condensate fraction n0.