SCATTERING OF SLOW-NEUTRONS FROM LONG-WAVELENGTH MAGNETIC FLUCTUATIONS IN UPT3

We report the observation of a low-energy contribution to the cross se ction of scattering of slow neutrons near the forward direction in the normal state of UPt3 at low temperatures. The results point to the ex istence of a weak component in the imaginary part of the dynamical wav evector-dependent susceptibility which may be represented approximatel y in a one-pole model with a wavevector-dependent relaxation frequency Gamma(q). In the low-q range of the measurements, Gamma(q) is up to a n order of magnitude lower than the nearly q-independent characteristi c frequency of a previously studied and well established dominant comp onent of the dynamical susceptibility. The new low-frequency contribut ion is interpreted in terms of the effect of low-lying fermion quasi-p articles in the presence of strong spin-orbit coupling.