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

We report the observation of a low-energy contribution to the cross section of scattering of slow neutrons near the forward direction in the normal state of UPt3 at low temperatures. The results point to the existence of a weak component in the imaginary part of the dynamical wavevector-dependent susceptibility which may be represented approximately 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 an order of magnitude lower than the nearly q-independent characteristic frequency of a previously studied and well established dominant component of the dynamical susceptibility. The new low-frequency contribution is interpreted in terms of the effect of low-lying fermion quasi-particles in the presence of strong spin-orbit coupling.