Failure of the Electronic Quasiparticle Picture for Nuclear Spin Relaxation in Metals

This paper investigates the range of validity of the quasiparticle picture by calculation of the temperature dependence of the nuclear spin relaxation time $T_1$. According to the simplest application of the quasiparticle picture, the electron-phonon interaction should produce a considerable deviation from the weak coupling law, $T_{1}T=\mathrm{constant}$. This deviation is not observed experimentally. Moreover, a more modern approach, based upon field theoretic techniques, predicts the constancy of $T_{1}T$ and hence restores the agreement between theory and experiment. Therefore, it is argued that the quasiparticle picture is a most inappropriate description of the effects of the electron-phonon interaction in metals.